Does Dave Duncan hate change-ups?

In the comments for my "eight types of pitchers" article, John noted:

Type 3 pitchers seem to be Cardinals even though they're just 4% of pitcher seasons they made up 12.5% of the Cardinals' 16-man staff last season. Also, while Type 2 pitchers make up just 18% of the MLB population, they made up 31.25% of St. Louis' staff last season. They seem to be doing that by avoiding Type 0, 4 and 7 pitchers. I wonder if this could be a personal preference by pitching coach Dave Duncan. Do you have data that suggests some MLB teams look for certain types of pitchers and/or convince pitchers to use a certain percentage of their stuff?

In other words, does Cardinals pitching coach Dave Duncan encourage his pitchers to become certain types of pitchers, and not other types? Duncan has been lauded on many blogs and baseball news sites over the past couple of years due to his staffs' repeated successes. He seems to have revitalized multiple pitching careers over the past few years, including Joel Piniero in 2009. Pitch F/X expert Dave Allen pointed out that Duncan's pitchers get more ground balls under his tutelage than they had before.

Is there a secret to Duncan's (perceived) success in reclamation pitchers? Does he turn pitchers into specific types that are more successful, on average, than other pitcher types?

John suggests above that Duncan's pitchers tend to be type 2 and type 3, but not types 0, 4, or 7, as compared to the league average last year. For those confused about the pitcher types, please read my article explaining the pitcher types. The types are derived from what I determine to be a pitcher's core and secondary pitches. All pitchers are assumed to throw the fastball as core pitch (I do not yet distinguish between two-seam and four-seam fastballs; coming soon, Dave). As a quick reference:

• type 0: change-up core; slider secondary
• type 1: cutter core
• type 2: slider core; change-up secondary
• type 3: slider and curve core
• type 4: curve core; change-up secondary
• type 5: change-up core; curve secondary
• type 6: slider core; no secondary
• type 7: splitter core; slider secondary

It turns out that John's observation is (mostly) correct.

I looked at 2005-2009, rather than just 2009. I counted all pitchers for each team that threw at least 20IP. This is plenty of playing time to establish a repertoire. Here is a list of all teams' pitcher types, by count of 20IP+ pitchers. First are the percentages, then the raw counts. I included averages and standard deviations for reference. The data is missing all pitchers who were traded midseason. Sorry.

Indeed, the Cardinals' pitchers are more likely to be type 3 (and also type 1) than an average team. The differences lie outside of one standard deviation from the norm. Likewise, the Cardinals' pitchers over one standard deviation below the norm for type 0, type 5, and type 6. The staff is within one standard deviation from the norm for type 2, type 4 and type 7.

Here is an excerpt of my full team type chart:

	T_0%	T_1%	T_2%	T_3%	T_4%	T_5%	T_6%
Average (1 STD)	7-19	2-10	12-24	1-8	8-20	4-13	39-26
Giants	10	6	17	6	11	7	41
Yankees	8	14	13	6	15	7	35
Cardinals	6	13	22	16	12	1	24

The sample size (71 pitcher seasons) is too small to conclude anything, but here are some possible explanations of what is happening:

1. Dave Duncan hates change-ups! Type 0 and type 5 are primarily change-up pitchers. Lots of really good pitchers have been type 5 (Greg Maddux & Tom Glavine, for example). However, very few of Duncan's pitchers fit this profile.
2. Dave Duncan doesn't care for young flame-throwers (or he reforms them quickly). Type 6 pitchers are the most common type of major league pitcher, by far. Many, if not most pitchers come up to the majors as hard-throwing type 6 guys, featuring a fastball, a slider, and not much else. There is a dearth of type 6 pitchers on Duncan's staff, although the number is not ridiculously low. They still make up 24% of his staffs (league average is 33%, and the Cubs form the high-watermark at 48%).

It actually doesn't take much analysis to see that Dave Duncan's pitchers throw fewer change-ups than any team in the baseball. FanGraphs has the aggregate pitch percentages by team year. Cardinals pitchers threw fewer change-ups that any other team in 2009, although they are somewhat higher in 2010 (but still solidly near the bottom).

This may just be confirmation bias, but it is entirely plausible that John is right, and Dave Duncan teaches his pitchers to throw curveballs, and not change-ups. As I mentioned in my previous piece, so far in 2010, Cardinals closer Ryan Franklin is throwing more curve-balls then even before, and would currently be classified clearly as a type 4 pitcher. Earlier in his career, Franklin used to be a slider/change-up kind of guy.

If Duncan tells his pitchers to throw curves as their off-speed offerings instead of change-ups, then that would explain why his staff has an unusually high number of type 3 pitchers. I assume that conventional wisdom would dictate that a pitcher should throw a slider or a curve. Maybe Duncan is teaching his pitchers to throw both a slider and a curve. If so, that would explain Cardinals' pitchers' improved ground ball rates.

Change-ups, when put in play, tend to result in fly balls (sorry I don't immediately know of a study proving it, but this makes logical sense). Thus it seems plausible that throwing fewer change-ups will result in fewer fly balls. Recent advances in DIPS (defense independent pitching statistics) seems to suggest that pitchers with high ground ball rates also give up fewer home runs per fly ball (as well as 0% home runs per ground ball).

In other words, in today's game, with short outfields walls and middle infielders who can hit one out, it may not make much sense to throw change-ups for any pitcher who does not have a swing-and-miss change-up.

Then again, this is just a theory. If you are interested in more data or have other ideas, drop me a line!

Looking Ahead

I trained a basic model to adjust projected FIP using a pitcher's type. For the same 2005-2009 span, pitchers tended to underperform my projections (ie post higher FIP), if they had types 0, 2, 5 and 6. The worst-performing type was type 5. The best-performing type was type 1 (cutter-throwers). There were also trends from previous years' types, again suggesting that type 0 and type 5 pitchers under-perform their expectations. However these are just weak trends. I will write something if/when I get something more definitive.

Strange Brew

I also ran a basic function, to figure out which teams had the most typical staffs and which had the strangest staffs, by pitcher type composition. The Cardinals have had the most unusual staff in the majors during 2005-2009. Closely followed by... the Brewers. So John was right in another respect. The Cardinals have the most unusual composition of pitchers in the majors during the past five years.

The most typical staff was that of the Giants, followed by the Florida Marlins.

Expect an article on this topic, as well.

Starter vs Reliever

I was looking at ways to show (in a chart or map) how pitcher performance changes when pitcher change their type (ie learn or forget different pitches). I soon realized that I needed a single rate stat to measure how a group of pitchers' performance changes. Of course, this stat has to be FIP. However, there are starter/reliever issues that need to be considered first.

This problem has been considered before, and I not aim to shed much new light on it, except to show a couple of graphs based on recent data.

To establish the difference between starter and reliever performance, there is a long, comprehensive article from Steve Treder on THT that often gets cited. It looks at starter/reliever differences throughout baseball history, and concludes that the difference between starter and reliever performance is consistently about 8% of ERA (about 0.3-0.4 on the ERA scale). However that is not the question I need to answer. Instead, I want to compare a group of pitchers' collective performances, and adjust for the groups' tendencies to be throw innings as starters or as relievers. Since starters are, collectively, better pitchers than relievers, the adjustment has to be larger than 8%.

A more useful study is Tom Tango's work on his blog. He looks at the same pitchers as starters and relievers, making several important adjustments. His conclusion is that pitchers have 17% more strikeouts, and 17% fewer home runs as relievers, as they do as starters. They also have a 17% better BABIP. He concludes that the same pitchers are "about a 1 run per 9IP" RA better as relievers. I did something simpler (although less thorough), and came up with much of the same conclusions.

Consider the graph below. I mapped IP to FIP by bucketing real pitcher seasons by IP (2005-2009 data). The graph plots the median FIP for each bucket, along with the median start percentage (% of innings thrown by individual pitchers in starting roles) for each bucket.

By looking at the median, rather than the average, it is easy to see where the transition from starters to relievers really takes place (as measured by IP). This is like chemistry class. As we move up the IP scale, the average pitcher has higher energy. However he needs to overcome a state change to move from full time reliever to full time starter. The 60-120 IP buckets find him in a state of transition. Supposing that these pitchers are all of roughly the same ability, and their FIP is different only due to role changes, I use the data to fit the following function (where start % is on a 0-1 scale):

trFIP = a + (start %) * b

Here "trFIP" represents a "translated FIP," which I assume to be constant, on average, throughout the transition. The best fit is for a = 3.92 and b = 0.81. Therefore for any pitcher:

trFIP = FIP + 0.81 (1 - start %)

Now FIP is meant to reflect the pitcher's skills at striking out hitters and at (not) giving up walks, but it also predicts ERA very well (at least for FIPs near the league average). The translated trFIP does not have this property. As Tom Tango showed, BABIP changes along with SO9 and HR9, so ERA increases more than FIP increases as relievers become starters. A similar exercise for ERA led me to this formula:

trERA = ERA + 1.19 (1 - start %)

However, trERA is not very useful in comparing talent levels between groups of pitchers. I can explain why, but let's get back to comparing groups of pitchers...

Back to trFIP, here is the same graph as before, but also with trFIP buckets by IP:

The graph between 60IP and 120IP is not quite flat. This is not surprising, as I am taking the median of individual trFIP values within the buckets. Some pitchers get the full 0.81 penalty, but not all do. I am taking the median of a combined distribution.

My study is not as thorough as Tom Tango's, but I like my results. My median trFIP buckets imply that your typical 60-80 IP pitcher from 2005-2009 is a little bit better than a typical 100-120 IP pitcher from the same time period. I think this is actually true. A 60-80 IP pitcher is very likely to be a high-IP reliever, such as a closer or setup man. He could also be a swing man/long man, but bear with me. A 100-120 IP pitcher is likely a back-end starter or also a swing man/long man who ended up filling in for an injured regular. Although the former is likely a failed starter, he must have found success in the bullpen to get such heavy use. At the very least, it is plausible to suggest that the top-end relievers are better overall pitchers than low-end starters, if only slightly.

The again, I might be reading too much into a small matter. Going forward, I will use trFIP as a simple measure of overall performance, which is not biased by changes in starter/reliever usage. It creates a useful benchmark, but is not meat to as an absolute definition of differences between starters and relievers.

Here is the same graph of average performance by pitcher type, but using trFIP instead of FIP:

The type 1 (cutter throwers) pitchers are still collectively the best of the groups, but the difference between type 2 (slider throwers with secondary pitches) and type 6 (slider throwers without secondary pitches) is eliminated by the differences in the trFIP adjustment.

Also trFIP shows type 0 pitchers and type 3 pitchers to be largely ineffective. Type 0 pitchers are those whose core pitch is a change-up, but who also throw other pitches, often sliders (as opposed to type 5 pitchers who throw change-ups, but with curveballs as secondary offerings). Type 3 pitchers throw both a slider and a curve, or possibly a slurve. 

Type 3 pitchers are similar to both the type 2 slider-throwers and the type 4 curveball-throwers, but are more likely to become type 2 pitchers. Average trFIP seems to suggest that moving from type 3 to type 2 is not a bad move. This may just be confirmation bias, but the trFIP graph seems to suggest that throwing a slurve is, indeed, not an effective way to pitch. The fact that only 4% of pitchers feature both a slider and a curveball (but 70% featured one or the other) might also suggest the same. To be fair, successful type 3 pitchers Chris Carpenter and Adam Wainwright throw both a hard slider, and a slow curve. They are not throwing slurves. But most pitchers find more success with one pitch or the other, it seems.

Now that I have a way of comparing pitchers without concern for starter/reliever issues, I will look into what happens when pitchers switch types. Expect more charts, and maybe a confusion matrix.

Performance by Type (Intro)

Here is a graph of average pitcher performance by pitcher type, weighed by IP (over all pitchers with 20IP+ seasons).

There are non-trivial differences in strikeout rates, walk rates, and resulting FIP (HR9 rates are pretty constant, with a slight decrease for high-strikeout pitchers). However, there is not enough information in this one chart to jump to conclusions about what pitches to teach your 15-year old future major leaguer. Most clearly, pitchers can be successful by employing the methods of any of the eight pitcher types that I identified.

With selection bias playing a role, it is hard to conclude much from the raw differences between the performance of the pitcher types. However, the strikeout rates for type 6 and type 7 pitchers stand out, as compared to type 2 pitchers. Type 6 and type 2 are both fastball/slider pitchers, and yet type 6 pitchers have significantly higher strikeout rates. Type 6 pitchers surrender more walks, but still have lower FIPs than type 2 pitchers. However this difference can be explained by the facts that: type 6 pitchers throw harder fastballs on average (91.1 mph vs 90.1 mph), and they are much more likely to throw in relief (32% of innings vs 89% of innings).

Therefore, while it would be wrong to claim that type 6 pitchers are more effective then type 2 pitchers, it is fair to suggest that hard throwing fastball/slider pitchers (ie type 6) can be effective major leaguers by recording high strikeout rates, even if they can not control their walks very well. However, they are more likely to find success in relief roles with that repertoire.

I've often read that pitchers who are wild, inconsistent, or have limited repertoires should be relievers. I've also read that pitchers have the most value as starters, regardless of what they throw, as long as they guys out. Joba Chamberlain has become somewhat of a contentious issue in this regard. I have read some respected writers claim emphatically that he should be a reliever (because of his stuff, and his temperament), and others just as strongly claim that he has the most value as a starter (even if his performance per inning suffer from the move).

In earlier posts, I wrote that Chamberlain's dramatic drop in strikeout rates (from 10.6 SO9 in 2008 to 7.6 SO9 in 2009) can be explained largely by his drop in average fastball speed (from 95.0 mph to 92.5 mph). I argued that he never over-performed his expected SO9, relative to his fastball speed. Pitchers who throw 95 mph on average are supposed to have really high strikeout rates!

Now Joba Chamberlain is a typical type 6 pitcher, thinking about becoming a type 2 pitcher. He was a strong type 6 in 2008 (as well as in his magical 2007 debut). He became strongly type 2 in 2009 by throwing more curves, and adding a change-up. I guess he needed to expand his repertoire to make it as a starter.

In 2010, he is back to being a typical type 6 pitcher. Joba is throwing 65% fastballs, 32% sliders, 3% curves, and no change-ups. As a full time reliever, he has been pretty good so far (3.28 FIP and 8.7 SO9, albeit in only 10.1 innings). His fastball velocity isn't what it used to be, but it's up at tick at 93.1.  The jury's still out on Chamberlain, but if I had to guess, I think he's a type 6 pitcher to stay. He can still be effective as reliever without a 95 mph average fastball, but he may unfortunately have peaked.  That is strange to suggest for a guy who is only 24 years old, but he has lost some valuable velocity, and has not added much to his skill set.

Going forward, I will use my classifications to look at other pitchers' careers. This should illuminate some trends that simple averages of different pitcher types can not tell us.

Thankfully, pitchers change types quite often. In the last post, I mentioned some pitchers who have kept a consistent type for a long time. However, some pitchers re-invent themselves several times over a career. Rich Harden started out as as a type 2 (slider with secondary), then was a type 7 (splitter with slider) for several years. More recently, he is a type 5 (change-up with curve) pitcher. All Star closer Ryan Franklin has been a type 6 (fastball/slider only), type 2 (slider with other pitches), type 7 (splitter) and type 1 (cutter) in full seasons since 2002. This year, he is throwing lots of curve balls, and might end up as a type 4 (curveball with change-up backup)!

I look forward to analyzing this data more systematically. If you are interested in pitcher classifications for 2002-2009 (20IP+ seasons), they are alphabetically listed here. I have a notion of "weak membership" and "strong membership" for the categories, but I have not finalized it yet, so it's not included.

Pitchers: Eight Different Kinds

I often read that: "pitcher X is similar to pitcher Y, so he should a) have similar performance b) age at the same rate c) experience a similar injury history." Sometimes the comparisons are based on height, weight, handedness, or otherwise, but usually we think of pitchers as being similar, if they deliver similar performance. Without advanced stats, we might consider pitchers similar if they had similar won-loss records or had similar strikeout rates. Now, some of us might think of pitchers as being similar if they are fly ball pitchers or ground ball pitchers, or if their fastball moves inside or outside to right-handed hitters. However, these categories all seem to reflect performance, to varying degrees.

My goal is to classify pitchers, in a performance-neutral way, based on the pitches that they throw. I will present eight categories that comprehensively classify pitchers into types, based almost exclusively on the percentages that they throw their pitches (collected for 2002-2009 by BIS and for 2007-20010 by PitchF/X, all viewable on FanGraphs).

Why Classify by Pitches?

This is not to say that classification by factors other than pitch selection isn't interesting. We already classify pitchers by role (starter/closer/setup man) and by performance, in casual baseball conversations. However, I think it would be useful to classify pitchers by how they pitch, rather than by their results. In order to ask questions like "how do curveball pitchers age relative to other pitchers?" and "do fastball/slider pitchers make good starters?" it is necessary to have a way to classify pitchers based on what they throw, in a comprehensive and non-arbitrary way. (Declaring that a pitcher is a curveball pitcher if and only if he throws 25% curveballs seems too arbitrary, and unnecessarily restrictive.)

Why Eight Categories?

Baseball Info Solutions (BIS) tracked & classified a large number of pitches for 2002-2009, giving us insight into how each pitcher's repertoire broke down over those years. This is the data that I use to derive my classifications. Since 2007, MLB has contracted Pitch F/X (same guys who do the virtual first-down line for NFL games) to track pitches in all major league stadiums. Their data is more comprehensive (Pitch F/X also tracks two-seam (sinking) fastballs), but it is available on a much smaller sample. (All of this data is hosted on FanGraphs and can be viewed for free.)

BIS recognizes seven pitches: fastball, slider, cutter, curve, change-up, splitter and knuckleball. A few months ago, I developed a system to determine which of these were a pitcher's "core pitches," which were "secondary pitches," and which were pitches that he did not really throw (even if they had pitch counts over 0% according to BIS. Consider a pitcher who throws 70% fastballs, 25% sliders, and 3% change-ups and 2% curveballs. His core pitches are fastball and slider, while the others are not relevant. Now if he threw 70% fastballs, 20% sliders, 9% change-ups and 1% curveballs, we might says that fastball and slider are still his "core pitches," but "change-up" is now a "secondary offering." I classify pitchers based on these distinctions.

Over the course of a season, almost all pitchers' repertoires can be described as:

• core offerings: Fastball + 0-2 other pitches
• secondary offerings: 0-3 other pitches 

Actually, most pitcher seasons fall into an even tighter rule:

• core offerings: Fastball + 1 other pitch
• secondary offerings: 0-2 other pitches

Therefore, the simplest way to describe a pitcher's repertoire is to name his core offering (ie the pitch he throws most often, not including his fastball). There is a strong correlation between the core offering and his likely secondary pitches. Pitchers who throw lots of curveballs tend to throw some change-ups, as well. Pitchers who throw splitters usually also throw sliders.

Since there are six possible pitches available as core offerings (not including the fastball, which everyone throws), there are six obvious categories. However, the knuckleball is so rare in today's game that I do not create a category based on it. Instead, there are five obvious categories (slider, cutter, curve, change-up, and splitter). In practice, more categories are needed, since not all pitchers who throw fastballs and sliders are truely similar, etc.

Using a simple clustering algorithm (SimpleKMeans using manhattan distance for the "core" and "secondary" pitches), I came up with seven categories. This was enough to get a category focused on cutters. I still needed a category for splitters, so I created one manually (by computing a centroid for all pitchers who throw a splitter). Then I tuned the weights and added other small considerations, so that the selection criteria for the categories were more intuitive.

Eight Pitchers

Here are the eight pitcher categories that I came up with, along with explanations, examples, and obvious tendencies.

Type 0: Changeup (Slider & Curve backup)

(14% of pitcher seasons)

The types start with 0, since nerds number their days 0-6.

A typical type 0 pitcher throws 61% fastballs, 18% change-ups, 11% sliders, and 6% curves. They are most similar to type 5 pitchers, although they are more likely to throw the slider, less likely to throw the curve, and less likely to be starting pitchers.

Sucessful type 0 pitchers include:

• Pedro Martinez (until 2006, when he became a type 5)
• Felix Hernandez
• Johan Santana (until 2007, when he became a type 5)

Type 1: Cutter (no common backup)

(4% of pitcher seasons)

A typical type 1 pitcher throws 56% fastballs, 20% cutters, and various other pitches depending on the pitcher. Type 1 pitchers are not similar to any other pitchers, but they are more likely to throw curveballs that sliders, which makes them somewhat similar to type 4 and type 5 pitchers. Type 1 pitchers are likely to be starters, but some very successful closers are type 1 pitchers.

Successful type 1 pitchers include:

• Mariano Rivera
• Jon Lester
• Andrew Bailey
• Roy Halladay since 2007 (previously a type 4 pitcher)

Type 2: Slider (Change-up and Curve backup)

(18% of pitcher seasons)

Type 2 pitchers are fastball/slider pitchers, who also throw other pitches at non-negligible rates. A typical type 2 throws 62% fastballs, 18% sliders, 10% change-ups and 7% curves. Type 2 pitchers are similar to type 6 pitchers, but type 2 pitchers are those that also have secondary offerings. Type 2 pitchers are more likely to be starters than type 6 pitchers, and also don't throw as hard.

Successful type 2 pitchers include:

• CC Sabathia
• Zack Greinke
• Jake Peavy

Type 3: Curve & Slider (no common backups)

(4% of pitcher seasons)

Type 3 pitchers throw both a curve and a slider frequently enough for them to both be considered "core pitches." A typical type 3 pitcher throws 57% fastballs, 18% curves and 16% sliders.

When I first saw this category, I thought these might be pitchers who throw a "slurve," or those pitchers who switched breaking pitches within a season. Those would end up in this category, to be sure, but successful type 3 pitchers recently included some very good pitchers:

• Chris Carpenter (2005 and 2009)
• Adam Wainwright (2005 and 2009, type 2 in between)
• Matt Morris

Type 4: Curve (with Change-up backup)

(16% of pitcher seasons)

A Type 4 pitcher throws 64% fastballs, 21% curves, and 9% change-ups. These pitchers typically throw very few sliders. They are most similar to type 5 pitchers (who throw more change-ups), although a type 4 pitcher can become a type 3 pitcher if he starts to throw more sliders. 

Successful type 4 pitchers include:

• Roy Halladay before 2006 (now he's a type 1 pitcher)
• Roy Oswalt
• Ben Sheets
• Justin Verlander 

Type 5: Change-up (Curve backup)

(8% of pitcher seasons)

A typical type 5 pitcher throws 62% fastballs, 23% change-ups, and 12% curves. Type 5 pitchers are similar to type 0 pitchers in that both rely heavily on the change-up. However type 5 pitchers throw more curveballs, while type 0 pitchers throw silders. Also type 5 pitchers are the softest-tossing category that I considered, with a typical average fastball of only 89.1 mph.

Successful type 5 pitchers include:

• Cliff Lee (except 2007)
• Tim Lincecum
• Trevor Hoffman from 2002-2007 (currently type 0)
• Tom Glavine
• Greg Maddux

Type 6: Slider (no backup)

(32% of pitcher seasons)

Type 6 pitchers are your prototypical fastball-slider flame throwers. A typical type 6 pitcher throws 66% fastballs and 24% sliders, with 5% change-ups and no curveballs. Type 6 pitchers are similar to type 2 pitchers, but they throw fewer secondary pitches. When a slider-throwing type 6 pitcher starts throwing a secondary pitch, be becomes a type 2 and vice versa.

Type 6 pitchers are the most common pitcher in MLB today, representing 32% of pitcher seasons from 2002-2009. They are the most common relief pitchers in baseball, but some successful starting pitchers were also type 6 pitchers. Type 6 pitchers often become type 2 pitchers, but here are some successful type 6 pitchers who have remained so throughout their careers:

• Randy Johnson
• BJ Ryan
• Joe Nathan
• Brad Lidge
• Josh Johnson 

Type 7: Splitter (Slider backup)

(4% of pitcher seasons)

Type 7 pitchers have become a rare breed, still I felt compelled to force a category for them. Splitter throwers have been some of the most successful pitchers of the last 20 years, so even if there are very few left in 2010, they are still worth separating them from the type 6 pitchers that they most resemble. A typical type 7 pitcher throws 60% fastballs, 15% splitters, and 10% sliders. 

Successful type 7 pitchers include:

(4% of pitcher seasons)

• Roger Clemens
• Curt Schilling
• Hideo Nomo
• Armando Benitez

Of course, Bruce Sutter is most famous for "inventing" the splitter. His version was thrown very hard, as a fastball with movement. Pitchers before him threw a split-finger pitch called a forkball, but that was more of a change-up. For some reason, the splitter has lost its popularity in the last few years, despite some of the best pitchers in recent history being avid proponents.

Typical type 7 pitchers throw even harder (91.5 mph average fastball) than typical type 6 slider-throwers (91.1 mph average fastball). This suggests that only hard-throwing slider-type pitcher ever become splitter-throwers. For some reason, recently very few type 6 pitchers have attempted this transition. There are probably good baseball reasons why this is has been the case, but I don't know what those might be. I'm an expert on machine-learning classification, not pitcher mechanics!

Hopefully the classifications and examples sound intuitive & intriguing. FWIW, here is a list of all 2009 pitcher seasons (over 20IP) with type classification (seasons ranked by pitcher VORP).

Despite the fact that these classifications are made without any consideration for performance, there are definitely differences in average performance between the eight categories of pitchers. I will follow up to discuss some of those differences. However, I think the most useful aspect of my categories is their descriptive quality. Although they rely (almost exclusively) on comparing % breakdowns of pitches thrown, the categoires can be described simply and intuitively. Not all pitchers fit neatly into a category, but very few pitchers don't belong in any category at all. I have made simplifications by ignoring knuckleballs and different fastball types, but without these simplifications, the list of categories might be even longer. My aim is to be insightful, but simple. 

I'm working on a site to host some of my data, including profiles for all pitchers, and their classifications by pitcher type. However, this will take some time. If you are interested in the type breakdown for a specific pitcher, take a look at this list, or contact me!