Originally posted on Fangraphs  |  Last updated 11/21/11

The Cubs need to prioritize. As a struggling franchise, they need to significantly overhaul their roster and farm system. A possible trade chip, as Buster Olney wrote last monday, is Matt Garza. This year was excellent for Garza; to highlight a few of his achievements, he posted career bests in WAR, FIP-, and xFIP-.

Much of his success can be traced to an improved strikeout rate. He struck out opposing batters 23.5% of the time, placing him right in between Roy Halladay and C.C. Sabathia for 12th among all qualified starters. In addition to an increased strikeout rate, we also know that he has been depending much more heavily on his off-speed and breaking stuff. Therefore we can attribute his great 2011 performance to his decreased usage of his fastball.

But is it that simple?

Just two years ago, Matt Garza posted a strikeout rate nearly as good as in 2011 — 22% of all PA’s. Factor in the difference in run environments and the switch from the AL East to the NL central, and his rate from this year is no longer unprecedented. He wasn’t limiting his fastball usage either back then, throwing about 70% fastballs according to my classifications, so it’s not as simple as saying that a drastic change in his fastball usage definitively led to the drastic jump in strikeout rate. He’s seen this kind of spike before, even without changing the amount of fastballs he threw, so we have to look deeper to see if there’s anything else going on.

We like to think of strikeouts as immune from luck. They are paramount in sabermetric analysis of pitchers, and have a very strong relationship with all major run estimators. And while the importance placed on strikeout rate is the correct decision for these metrics and analyses, it’s important to be mindful of the fact that lucks plays a role in strikeout rates too. No, strikeout rate is not nearly as inconsistent as BABIP or HR/FB, but there are times when a pitcher’s observed strikeout rate significantly diverges from his true talent strikeout rate. This is because the ability to record strikeouts is not really one ability, but a composite of skills. The pitcher’s prowess in getting swings and misses, called strikes, and even expanding the zone all affect overall strikeout rate. Of course not all of these skills are equally important.

A skill that tells us a lot about a pitcher’s strikeout ability is whiff rate — the amount of whiffs divided by the total number of pitches thrown. Here are Garza’s whiff rates and contact rates (whiff/swings), split up by year:

year whiff contact 2008 0.08 0.83 2009 0.08 0.81 2010 0.08 0.83 2011 0.12 0.76

With a huge jump in strikeout rate we would expect to see a corresponding increase in whiff rate — and that’s exactly what we see with 2011. There is a clear improvement in his ability to get swings and misses in some parts of the zone:


The extra whiffs that he’s getting in 2011 are right on the outside edge of the strikezone to a right-handed batter — the location where he’s throwing many of those additional breaking balls. Dotted lines indicate the strikezone and the bands indicate confidence.

But we still haven’t explained why his strikeout rate was so high in 2009. Turning our focus to called strike rates, we find the following proportions of plate appearances that ended in a called strike three (denoted by cs rate):

year cs rate 2008 0.05 2009 0.06 2010 0.04 2011 0.04

But the opportunities in which Garza can record a called strikeout are affected by other variables — like whiff rate — that we want to ignore. If we only look at pitches that can end up as a called strikeout — pitches thrown in two-strike counts that are not swung at — we find the following proportions:

year cs rate oppurtunities 2008 0.13 296 2009 0.12 403 2010 0.09 385 2011 0.10 305

A visual examination yields a bit of a mess:


Again, only looking at pitches here that could potentially result in a called third strike.

The table helps to explain some of the variation in Garza’s strikeout rate. While his called third strike rates were similar in 2008 and 2009, he had many more opportunities for such a result in 2009. This can be explained by the fact that more of his pitches came in two-strike counts in 2009 (27.6%) than 2008 (26.1%). In 2010, he simply did not have as many of his potential called third strikes turn into actual called third strikes. This had a significant effect on his strikeout rate; if we apply his 2009 called strike three rate to his 2010 number of opportunities, we would expect him to have 46 called strikeouts — 12 more than he actually had. These 12 additional strikeouts would have bumped his strikeout rate from 17.5% to 19%. Given the small samples at play here with called strike three opportunities, luck can have a larger role than what we expect. A significant test between the two proportions (2009 and 2010) yields a result that is not significant at a 95% level.

Often times explanations are simply drummed up to explain so-called “breakout” years. Many of these are simply the result of our own cognitive dissonance — it just feels so wrong to a attribute a breakout performance to luck, so we craft our own narratives to reduce the mental tension. Most of the time these explanations are just that — rationalizations with a sprinkle of truth and a dollop of imagination. But not every time. Jose Bautista, for example, completely revamped his swing. Matt Garza looks like he could be another legitimate improvement. Is he the 5 WAR stud he was in 2011? No, we can’t just throw out the rest of his career. But there is reason to believe that he is better than he was before. His peripherals entirely support his performance and can be explained by a shift in pitch selection. Of course it’s possible that the league adjusts in 2012, but there is no reason to dismiss 2011 as a fluke.

References and Resources

*PITCHf/x data from MLBAM via Darrel Zimmerman’s pbp2 database

*Plate discipline statistics calculated by author

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