Passionate Chicago Cubs fans questioned the strike zone of the home plate umpire when their team finally made it back to the World Series after Corey Kluber’s fantastic performance. Ian York, as he has done in the past, used PITCHf/x to investigate the strike zone of Larry Vanover to determine if Chicago’s fans have a legitimate claim or if the umpire deserves credit for a job well done.
In Game One of the 2016 World Series, Cleveland’s Corey Kluber outpitched the Chicago Cubs’ Jon Lester en route to a 6-0 win. Some Cubs fans complained that home plate umpire Larry Vanover’s strike zone was inconsistent, with Kluber getting some calls that Lester did not.
When asking strike zone questions, it’s important to look at the strike zone that umpires universally call, rather than the rule-book zone. The de facto strike zone, the one batters and pitchers are actually used to seeing, approximates the rule-book zone, but has rounder corners, bulges on the sides, and is slightly different for right- and left-handed batters. By using PITCHf/x to locate all of 2016’s called strikes and balls, and drawing a line through the region where those calls were equally likely, we can outline this de facto strike zone and ask if Vanover’s calls fit with players’ expectations.
Here are the called strikes (in red) and balls (blue) that Cleveland batters saw. The de facto strike zone is the polygon in the middle:
Cleveland’s left-handed batters saw 39 pitches, but only 20 of them were called by the umpire, and all of those calls look pretty reasonable. (Pitches that fall right on the line have about a 50-50 chance of being called a ball or a strike, since that’s how the line was defined, so it’s hard to call those wrong or right. Note also that PITCHf/x is not 100% accurate. At best it is probably only accurate to within an inch or so, and the system occasionally makes data errors that are glaringly wrong.)
Batting right-handed, Cleveland’s offense saw three or perhaps four extra strikes called on them, two or three just below the zone and one outside. There was one ball called well inside the zone (on the bottom outside edge) and one just below the top of the zone that should probably have been a strike.
Here’s the same graphic for the Cubs batters:
Left-handed batters had one extra ball handed to them (near the top of the zone) and no extra strikes. Right-handed batters received one, and perhaps two, extra balls, and no extra strikes.
Overall, Vanover called a fairly good game; of 178 calls, he made between five and seven errors. That’s 96.1% to 97.2% accuracy, which today is a typical level for an umpire. All in all, Cubs pitchers came out slightly ahead, with more extra strikes than balls, while Cleveland pitchers had no extra strikes given to them, but did have two strikes called balls. Although this look at Vanover’s strike zone doesn’t account for the context – a missed strike call on a 3-2 count is more important than on 0-2 – it’s hard to argue that Lester was particularly harmed by the home plate umpire in this game.