January 16, 2017
New Year's Resolutions: Hitters' Plate Discipline
In this series, we’re investigating the outcomes when baseball players made what appear to have been New Year’s resolutions to do something differently in 2016. But unlike the rest of us, who try to waste less time watching TV or learn another language, we’re looking here at specific baseball outcomes. The first article considered batters who hit markedly more (or less) to the opposite field in 2016 than in 2015. The next two looked at batters who hit more or fewer balls on the ground and pitchers who induced more or fewer grounders.
And I’ll admit, framing these as New Year’s resolutions is a bit of a stretch. There probably aren’t a lot of baseball players who said last January 1 that what they really wanted to do in 2016 was to hit more balls in the air. Today, though, I’m going to tackle one that seems plausible: Better plate discipline.
It’s hard to imagine a non-Vlad Guerrero hitter who wouldn’t want to improve his plate discipline. Forcing pitchers to throw strikes means more chances to get a pitch you can drive. Reducing strikeouts and increasing walks, those are good things too. It’s pretty tough to identify a downside of plate discipline.
Measuring plate discipline is tricky, though. Strikeouts and walks? Often they go hand-in-hand rather than in opposite directions. Paul Goldschmidt, for instance, was 10th in the National League in strikeouts and first in walks last season. Among batting title qualifiers last year, the correlation between strikeouts and unintentional walks was positive 0.35—as strikeouts went up, walks did too.
So we can’t point to a hitter with a lot of walks or one with few strikeouts and automatically say, “Good plate discipline.” And, of course, walks and strikeouts are a product of pitchers as well as hitters. I remember somebody claiming that Manny Ramirez didn’t have very good plate discipline but he walked a lot in his prime simply because nobody wanted to risk throwing him strikes.
PITCHf/x can help here. We know whether or not every pitch a batter saw was in the strike zone. We know whether or not the batter swung at the pitch. Swinging at pitches in the strike zone is good. Watching them go by and get called as strikes is not. Similarly, swinging at pitches outside the zone is bad. Letting them go for balls is good. (Hold off before posting comments about the problems with those last four sentences; I’m getting there.)