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

Friday, September 10, 2010

Tim Lincecum: home runs, strikeouts and fastball speed

Whatever happened to Tim Lincecum? His 3.69 ERA over 185 IP is pretty good and his FIP of 3.33 is even better, but both are a well below his 2008-2009 level, when he deservedly won two NL Cy Young awards. His strikeout rates are down. His walks are up. He is also allowing more home runs.

By far the biggest difference between 2008-2009 and 2010 for Lincecum have been his home runs given up. He gave up home runs on 6% of fly balls in 2008-2009, but 10% of fly balls in 2010. Tim's xFIP (FIP with league-average for HR per fly ball) is only slightly up from 2008-2009.

So if someone asked you: "what's wrong with Tim Lincecum in 2010?" you would tell him that his luck with fly balls going out has turned for the worse. Then you would debate how much a pitcher controls his HR/fly ball rates. But other than home runs given up, has anything else changed about Timmy the Freak?

Eric Seidman of Baseball Prospectus recently wrote an article on Lincecum, attempting to break down the differences in his repertoire between 2010 and 2008-2009. It's unclear what changed, other than the drop in fastball speed, and also a decrease in fastball movement. Seidman goes on to suggest that, if Lincecum's fastball is slower an "has less bite," then it may make the rest of his pitches less effective, even if they are the same pitches as before.

There are a lot of moving parts here, so let's just look at his declining fastball speed compared to his declining strikeout rates. Of all the changes, these are the most easily noticeable "cause" and "effect." Numbers from Lincecum's FanGraphs profile.

Year SO/9  average FB % fastballs
2007 9.2 94.2 69%
2008 10.5 94.1 66%
2009 10.4 92.4 56%
2010 9.7 91.3 55%

The trend is weak, but is looks like Tim Lincecum's strikeout rates are declining with his fastball slowing down. Lincecum improved as a strikeout pitcher from his 2007 rookie year, but is now probably maximizing his strikeout ability, relative to his physical skills. As the physical skills decline, so will his ability to strike batters out.

Why am I looking at fastball speed in predicting strikeout rates, and not various other pitcher skills or characteristics?

In a series of studies I did last winter I found that, of all the non-performance pitcher attributes, fastball speed was by far the most predictive in terms of predicting strikeout rates. I can predict a pitcher's strikeout rate (given a reasonable IP cutoff) with R=0.52, given just his average fastball speed.  The predictive power only goes up to R=0.59 if I also look at what other pitches he throws, his league, his age, his weight, and whether or not his is left handed. Of those factors, the league and handedness are by far the most helpful. See my old article here for more details.

The most important relationship that I discovered in my research was that 1. fastball speed predicts strikeout rates to a significant degree 2. the relationship is non-linear.

Here are fastball speeds vs strikeout rates 2002-2009 pitchers. Strikeout rates are fit by a quadratic function (ie square of the fastball speed). Note the discrepancies by league:

A fastball velocity drop from 95 mph to 90 mph in the NL (in blue) is worth a strikeout rate drop from 9.0 SO/9 to 6.5 SO/9. That's a big difference. For a starting pitcher, that's a drop from being an elite strikeout pitcher to being league average.

Tim Lincecum has dropped from a 94.1 mph pitcher to a 91.5 mph pitcher. According to the graph above, that should be worth a strikeout drop of about 8.5 - 7.0 = 1.5 SO/9. Even for someone who strikes out ten batters per nine innings, a 1.5 SO/9 drop is enough to taking him down from elite pitcher to just very good.

Tim Lincecum is not a typical pitcher. He over-achieved his fastball-based strikeout projection at 94 mph, and he's over-achieving his strikeout projection at 91.5 mph. But the strikeout drop is still there. If Lincecum's fastball declines further, he won't any longer be a ten strikeout per nine innings pitcher. To record sub-3.00 ERA's, he'll have to bring down his walk rates from around 3.0 BB/9 to more of a Cliff Lee type level, or he will have to get lucky with keeping fly balls in the park at well below the league average.

He is not so old that decreases in fastball speed are inevitable, but I'm guessing that Tim Lincecum is too young to increase his fastball speed, the way that Zach Greinke did 2005-2007. Nor does he have the strikeout rate advantage of being left-handed (worth about +1.5 SO/9 for the same fastball speed, according to my study).

There are many components that go into being a great pitcher. But strikeout rates and walk rates are the two factors that pitchers have the most control over. I'm not saying that Lincecum's 10.0 SO/9 rates from the last couple years were a fluke. But he will have trouble maintaining those into the future as his fastball speed has already declined. Look for him do decrease his walks. If he is not able to do so without further decreasing the strikeout rates, Tim Lincecum can't be considered the best pitcher in baseball going forward.