Should Strasburg pitch to contact?

After Stephen Strasburg‘s first start back from Tommy John surgery on Tuesday, there were several interesting articles describing how he has changed as a pitcher.  For example, Tom Boswell of The Washington Post quoted Strasburg:

I’m really trying to be a pitcher out there, not just light up the radar gun every time… Guys don’t want to get to two strikes against me, so if you make quality pitches early in the count, you can get quick outs… I think my command of my fastball is better than it was before… because I don’t try to dial it up every time.

Boswell then added:

If all this sounds familiar, it should. It’s the same theory of better efficiency that made Jordan Zimmermann so much better this season… For one night, almost everything Strasburg set as goals for himself for the past year — better efficiency and lots of soft contact rather than long-at-bat strikeouts — was on display instantly.

Boswell’s colleague at the Post, Adam Kilgore, spelled out some of the differences:

Rather than throwing his fastball at 98 and 99 miles per hour, the Nationals and Strasburg have decided he is better served throwing 96 and 97… He averaged only 11.2 pitches per inning, lower than any of his starts in 2010. He averaged about 96.7 miles per hour with his four-seam fastball and 95.1 with his two-seamer. He focused not on striking out Dodgers hitters, but on inducing weak contact. He struck out four of the 17 hitters he faced.

Jeff Zimmerman of Fangraphs did a PitchFX analysis of his first start and found that Strasburg’s fastball speeds were about 1 mph slower than last year’s. He also notes that his changeup has a new spin and breaks down less than before.

It appears that the Nationals strategy for Strasburg aims for:

• Lower velocity
• Fewer pitches per batter
• Fewer strikeouts and walks
• Weak contact
• More balls in play
• With the result of longer outings and more innings pitched per start.

Is this approach likely to succeed?  There are some parts of this question I’m really not equipped to answer, such as whether pitching to contact may reduce his risk for injury. But sabermetrics does provide tools that allow us to address the narrower question of whether pitching to contact can allow Strasburg to work deeper into games.

The math of working deeper

There are three ways for a pitcher to work deeper into games: he can throw more pitches per game, he can throw fewer pitches per batter, or he can see fewer batters per out. Presumably, the Nats aren’t planning to have Strasburg throw many more pitches per game, so their approach will focus on the latter two.

There’s a close relationship between strikeout rates, walk rates, and the number of pitches thrown per batter.  I ran a linear regression on all starting pitchers with at least 60 IP during 2008–10 that gave the following equation relating pitches per batter faced to walk rate (walks per batter faced) and strikeout rate (strikeouts per batter faced):

Pitches/BF = 3.19 + 3.4 * walk rate + 1.9 * strikeout rate. (R^2 = .52, n = 274)

For example, if pitcher A has a walk rate that’s 5 percentage points lower than pitcher B and a strikeout rate that’s 10 percentage points lower, he’s likely to throw 3.4*.05 + 1.9*.10 = .36 fewer pitches per batter. So a pitcher can throw fewer pitches per batter by getting earlier contact and fewer walks and strikeouts.

The main way a pitcher can see fewer batters per out is to lower his opponents’ on-base average.  Reducing the walk rate is a very effective way to lower the on-base average. On the other hand, reducing the strikeout rate will, all else equal, tend to raise the opponents’ on-base average. On-base average can also be reduced if the pitcher can lower the opponents’ batting average on balls in play.

An example: Jordan Zimmermann

Boswell mentions the changes that Jordan Zimmermann has made this season as a prototype for what the Nats would like Strasburg to do. How has Zimmermann changed?

Comparing his season in 2009 before the Tommy John surgery with his 2011 season, we first note that he isn’t throwing more pitches—in fact, his pitches per game dropped slightly, from 98.4 to 94.8. He did reduce his strikeout rate (from 23.5% to 18.7%) and his walk rate (from 7.4% to 4.7%), and raised his contact rate. Along with getting fewer strikeouts and walks, he’s reduced his pitches per batter from 4.03 to 3.72, a little bit larger reduction than predicted by the formula shown above.  By throwing fewer pitches per batter, he’s been able to pitch to about one more batter per game (an increase from 24.4 to 25.5). Finally, his reduction in walks along with drops in home runs given up and in opponents’ batting average on balls in play (from .339 to .296) has allowed him to reduce his opponents’ on-base percentage (from .332 to .294) in spite of the reduction in strikeouts. The net effect—he’s increased his average outing from 5.71 innings to 6.21 innings, or about two additional outs per game.  The results on his performance also appear to be excellent, with his ERA dropping from 4.63 to 3.18.

It sounds like a resounding success for the “pitch to contact” philosophy, but there are some caveats. Comparing his batting average on balls in play for the two seasons, it’s 2009 (.339) that’s unusually high, while 2011 (.296) is quite close to the league average (.294). We normally expect pitchers with high BABIP to revert toward more average numbers, so that part of JZim’s improvement would have been predicted regardless of any change in pitching style.

Furthermore, other than getting fewer home runs per fly ball, JZim’s batted ball statistics don’t necessarily indicate that his batted balls were getting weaker contact. His ground ball rate was lower in 2011 than 2009, as was his infield fly rate. On the other hand, his line drive rate was lower.

We also think that there tends to be a large “luck” component to home runs per fly ball; JZim’s rate of 5.9% is sixth lowest in baseball and will probably revert to a higher level. Two sabermetric measures that remove these components of luck (FIP, which removes BABIP, and xFIP, which also removes the effects of home runs not accounted for by fly ball/ground ball rates) show much less improvement than his ERA—indeed, his xFIP was actually higher in 2011 than in 2009 (3.77 versus 3.35). These statistics raise questions about how much of his improvement in performance can be attributed to his new pitching style.

Nevertheless, the advanced metrics still show JZim to be an above average pitcher (his FIP for 2011 is 3.16, or very close to his ERA, while his xFIP is higher at 3.77), and he is successfully pitching deeper into games than he did before his surgery.

The case of Justin Verlander

Kilgore mentions the improvements made by Justin Verlander this season as another prototype for Strasburg’s pitch-to-contact approach. Indeed, in 2010 Dave Cameron of Fangraphs discussed Verlander as an example of a pitcher whose value was limited by his inability to go deep into games.

This season, Verlander has not only been much more successful, but he has pitched deeper into games, averaging 7.39 innings per game compared to 6.80 last season. But looking at the details, it’s not clear that his new approach can be described as pitching to contact. While he’s lowered his walk rate from 7.7% in 2010 to 5.8% this season, he’s also raised his strikeout rate (from 23.7% to 26.3%), so his contact rate has actually been essentially unchanged.  Similarly, his pitches per batter (4.05 last season, 4.08 this season) have hardly changed. What has changed, besides the improvement in both strikeouts and walks, is his opponents’ batting average on balls in play, which fell from .289 to an almost absurdly low .236, with a corresponding drop in on-base percentage from .291 to .240.  Setting aside the question of whether such rates are sustainable, the bottom line seems to be that he’s pitching deeper into games because he’s getting more batters out. That’s great, but if there’s a secret formula for doing that, every pitcher in the world would want to copy it.

My takeaway from looking at Verlander is that he’s pitched great, but I don’t see his performance as especially relevant for evaluating the Nationals’ pitch-to-contact philosophy.

What to expect from Strasburg

Of course, it’s foolhardy to extrapolate from one pitcher’s experience to another’s. Nevertheless, Zimmermann’s experience does provide one example of what might happen with Strasburg if he continues to pursue the pitch-to-contact philosophy. So I thought it would be interesting to build a scenario for Stephen based in part on JZim’s experience.

For this scenario, I’m going to make the following assumptions for 2012:

1. Strasburg’s strikeout rate drops (relative to his 2010 rate) by the same proportion that JZim’s rate dropped from 2009 to 2011 (20%). In other words, his strikeout rate would drop from 33.6% to 26.7%.
2. Similarly, his walk rate drops by the same proportion that JZim’s did (37%). That is, his walk rate would drop from 6.2% to 3.9%.
3. All of his other statistics (such as hits, home runs, etc.) revert to the major league average rates excluding walks and strikeouts. (For example, Strasburg’s BABIP in 2010 was .319; it would drop to the major league average, which is .294.) Because Strasburg’s 2010 rates for in-play events were generally close to the league average anyway, and these rates should be heavily regressed for small samples, this seems like the best projection for these components.
4. For playing time, I’ll assume that he gets the same number of starts that JZim had this season (26) and averages the same number of pitches per game that JZim threw (94.8). Note that Strasburg averaged only 89.4 pitches per game in 2010, so this is assuming an increase in pitches per game of 6%.
5. I use the regression coefficients that appear above to calculate the change in pitches per batter.
6. Finally, I’ll use the “Base Runs” formula to project the results of these assumptions.

Based on these assumptions, Strasburg does pitch deeper into games, facing an average of 25.6 batters, compared to 22.8 in 2010. About half of this change comes from throwing more pitches per game, the other half from lowering his pitches per batter from 3.92 to 3.71.  His opponents’ on-base percentage stays about the same (.265 versus .268 in 2010) as the reductions in walks and in BABIP offset the reduction in strikeouts. Consequently, his average innings pitched per game increases from 5.67 to 6.46, or a little more than two additional outs per game. Again, about half of this increase comes from assuming more pitches per game.

His opponents’ batting average would increase from .221 to .230 because the effects of fewer strikeouts more than offsets the assumed drop in BABIP. His runs allowed per 9 innings is projected at 3.11, compared to 3.31 for 2010.

All in all, this looks like a good move – a slightly better projected performance per inning and averaging about a 14% longer outing per start. What might go wrong? The assumption that he lowers his walk rate by 37% is awfully strong. If, for example, his walk rate didn’t change at all, he’d be left with the negative effects of a lower strikeout rate with no offsetting improvement in walks, hurting his performance.

If we assume that his average pitches per game would have increased to JZim’s level even without the new pitch-to-contact approach, we’re left with relatively modest improvements in performance and length of starts that could disappear entirely if the improvements in control aren’t realized. Is it worth the risk to make this change?

If it were only the numbers I’ve been calculating, I’d probably not tinker with Strasburg’s approach. But Kilgore mentioned another consideration, that the Nationals believe Strasburg’s new approach will reduce the risk of injury. I don’t know whether there’s evidence for this view, but it seems plausible that throwing with a little less velocity could lessen the impact of pitching on the arm. If pitching to contact can keep Strasburg healthy, I’m all in favor.