The shrinking lefty zone and how the Indians can exploit it

Joe Roegele’s work on the size of the strike zone is fantastic stuff. He’s studied the zone for few years now and found that “between 2009 and 2015, the size of the called strike zone increased [...] the diameter of a baseball” at the bottom of the zone. This change, you may note, corresponds with some of the weakest offensive years in memory. In 2015, however, the size of the zone reached its maximum and has since receded; since then, home run rates have soared.

This is extremely interesting, but the air ball revolution and its relationship to the strike zone has been covered in great detail all over. What fascinates me is a different change.

Roegele points out that, in recent years, a decreasing number of strikes have been called on the outside for left-handed batters and more strikes have been called inside on right-handed hitters. As he notes, while the strike zone has erased its gains at the bottom, the outside edge of the box for lefties has also shrunk by about the same size — the width of a baseball. The opposite trend, inside strikes called on righties, has turned “what used to be handedness neutral [...] into an advantage for left-handed hitters in recent seasons,” according to Roegele.

So, if the advantage is there, have the Cleveland Indians been taking advantage?

Sample sizes matter here, and since the 2018 sample is approximately ¯\_(ツ)_/¯, we’ll consider 2017 first.

Of 6234 plate appearances in ‘17, 3055 were taken from the left-handed batters box (49 percent). The Indians preferred the advantage of platoon splits, allowing left-handed batters to face a pitcher of the same handedness in just 470 plate appearances; right handed hitters had more leeway, earning nearly three times as many plate appearances versus right-handed pitchers (1452). Overall, lefties struck out 540 times (17 percent of plate appearances) whereas righties struck out 613 times (19 percent); lefties walked 278 times (9 percent) and righties walked 326 times (10 percent; not counting intentional walks).

Based on these numbers, it does not seem Indians lefties got a benefit from a smaller zone or that righties struggled with an expanded zone. However, a majority of the Indians plate appearances came from the right side, as they faced right-handed pitchers most often (4037/6234 plate appearances, 64 percent) and tried to work the platoon advantage (69 percent of batters faced opposite-handed pitchers; league average was 52 percent).

Thus far, 2018 is noisier than your neighbor’s band. The Indians have faced more righties (257/366 plate appearances) and, accordingly, have hit from the left side more often (223/366; 61 percent). But consider Jason Kipnis and Yonder Alonso: the former has only been substituted for one plate appearance this season, whereas the latter had all but two plate appearances for first basemen before sitting on Monday. Although this is not cut-and-dried evidence of an eagerness to get more at bats for lefties, it is something.

Of course, the offense surely has not taken advantage of much of anything in the early going, but among all teams the Tribe is 13th in strikeout rate (23 percent, yes even with Bradley Zimmer’s >50 percent contribution) and sixth in walk rate (10.7 percent). It is too early for any real correlation between increased left-handed at bats and low strikeout rate/high walk rate to be meaningful, but it is noteworthy that even with more plate appearances, Cleveland’s lefties have accounted for 69 percent (27/39) of the team’s walks but just 63 percent of the strikeouts (53/84).

For Cleveland’s pitchers, looking at pitches from last year and this year, the trends do not seem to have adjusted for a different zone. For Corey Kluber, Carlos Carrasco, and Mike Clevinger, for example, the right-handers live on the lower outside corner against righties but show a less distinct pattern against lefties, mostly hitting the outside edge and lower inside corner. Trevor Bauer has a similar heavy output toward the lower outside corner on righties and also works that spot to lefties, but works more in the zone overall against left-handed competition. Josh Tomlin, who relies on pinpoint control because of his lack of velocity, stays in the zone more than anyone but generally has a similar profile as his peers.

With all righties in the rotation, sweeping breaking balls inside to left-handers or away from righties (who the starters face more often) is probably still the best course of action, even with the zone in that area diminished. And despite not showing a trend to maximize zone inefficiencies, the pitching staff has done a pretty good job (Josh Tomlin and his balky back notwithstanding). So far the Indians staff is 7th in strikeout rate (24.4 percent) and 2nd in walk rate (6.5 percent).

Looking back, it’s obvious platoons were the Indians go-to last year. Perhaps zone discrepancies are the inefficiency the team is seeking to exploit in 2018. It’s worth keeping an eye on, at least.