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

Saturday, November 28, 2009

Chien-Ming Wang, Edwin Jackson, Rick Porcello and projected K/9 rates

For all of the pitchers projected in the graph below (see previous post), I have summarized their data in a spreadsheet here. The data is sorted by "SO9_proj_error" which is just a measure of how much my projected K/9 value over (or under) estimated the actual strikeout rate.

The top rows of the chart show all the pitcher seasons for which my system had the largest under-estimates of strikeout rates. Two trends stand out:
  • Several pitchers appear on the top of this list multiple time (Eric Gagne, B.J. Ryan, Pedro Martinez, Uggie Urbina, Rich Harden, Mark Prior)
  • Most of these pitchers were dominant pitchers (at least for a few season).
  • Octavio Dotel is an interesting exception.
This seems to suggest that over-achieving one's projected K/9 rate is a repeatable skill, and a that this might be a valuable skill. It's not entirely clear how much this trend is separate from just the trend of high strikeout pitchers being very effective, however. Let's just leave it at that.

Now take a look at the bottom rows of the chart. Again, there is lot of repetition. We see the following starting pitchers several time at 2+ strikeout rate underachievement:
  • Kirk Rueter, Jorge Sosa, Carlos Silva, Aaron Cook, and Chien-Ming Wang
  • Edwin Jackson's K/9 underachievements have ranged between 0.85, 2.79 and 1.97 between 2007 and 2009.
Also, there are not many top-end pitchers that show up on the bottom of this list (the 2003 version of CC Sabathia doesn't count). Some good pitcher seasons, but none by pitchers that were dominant for a significant stretch of time. Again, it is difficult to completely separate this effect from just the negative effect of having low strikeout totals. However, some pitchers seem to possess the "skill" of consistently underachieving their projected K/9 totals. This is not one of the habits of highly successful pitchers.

To me, this suggests (though certainly doesn't prove) that Chien-Ming Wang and Aaron Cook should not expect to start striking out more batters, nor should they expect to become top-end starters. Carlos Silva, Kirk Rueter and Jorge Sosa should be good "comps" for these pitchers. Similarly, if Edwin Jackson is not able to get 7-8 K/9 next year, I would bet that he never will.

Projecting from their fastball speed and selection of pitches, Wang and Jackson should both be at least league-average K/9 pitchers (7 K/9). Cook projects a little less so at 6 K/9. However none of them are near their projected number, after several full seasons in the majors.

Now, let's consider Rick Porcello, the Tigers rookie who has been also come up in discussions about the future of low-strikeout pitchers. His K/9 average for 2009 was only 4.69, yet he is nowhere near the bottom of my chart. Based on his pitch data, he only projects to have averaged 5.54 K/9 in 2009. He underachieved his K/9 projection by 0.85. There are plenty of highly successful pitchers who have had similar figures (Mark Buerle, CC Sabathia, etc).

Why is Porcello's projected K/9 rate so low? He throws a league-average fastball (90.7 mph) and yet he throws it a 77.1% of the time. According to LM2 (the linear model for starting pitchers with league-average or below fastballs from my previous post), these are the dominant terms that contribute toward his low K/9 estimate. Let me reproduce the factors for LM2 below. I have skipped the terms that don't have a significant effect on the final value:

LM num: 2
SO9 =
- 0.0447 * FB_fg_per
+ 0.0083 * SL_fg_per
- 0.0159 * CT_fg_per
+ 0.0153 * CB_fg_per
- 0.0185 * CH_fg_per
+ 0.2423 * FB_fg_vel
- 0.2151 * rep_depth
- 0.1346 * rep_offerings

The "FB_fg_per" term corresponds to the percent of the time that Porcello throws fastballs. Multiplying 77.1 * -0.0447 = -3.45. So if Porcello decreases the number of fastballs that he throws to 55%, he will see this negative term decrease by 1.0. The model suggests that by throwing a third as many fastballs, Porcello can add about 1.0 K/9 to his projected total. The model favors curve balls and sliders for LM2 pitchers, so committing those "extra" 20% of pitches toward breaking balls can push Porcello's expected K/9 rate to the league average of 7.

Therefore, it seems plausible that Porcello can become a league-average strikeout pitcher by learning to throw more breaking balls. He can expect to achieve solid strikeout rates without developing a harder fastball.

I am not an expert on pitcher development, but I see no reason why this should not happen. Porcello is only 20 years old. He already throws sliders, change ups and curve balls over 5% of the time each. I don't know how scouts rate his secondary offerings, but I don't see why at least one of these can't develop into a good secondary pitch that Porcello can throw 25% of the time.

Porcello did not post a high strikeout rate in the minors, either, but was able to find success. Therefore, he already has the skills to pitch well without striking out many men. If he improves his strikeout rate, and there is a plausible reason that he can, Porcello has a chance to become a dominant pitcher.

Contrast his career path that of Chien-Ming Wang. He struck out lots of guys in the minors, and has the fastball to strike out guys in the majors. But for several years running now, he does not. That is unlikely to change.

Lastly, let's come back to Porcello's teammate, Edwin Jackson. Wang has the 93.9 mph fastball. However, he only struck out about 7.7 K/9 in the minors, and has had even lower totals in the majors (about 6.3 K/9). His strikeout totals are higher than Porcello now, but there is no reason to think that his will increase, after being lower than expected for several years. I'm not saying that this makes Porcello a more valuable pitcher than Edwin Jackson, but it is something for the Tigers to consider.

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