My writings about baseball, with a strong statistical & machine learning slant.

Sunday, May 2, 2010

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.

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