Starlin Castro’s plate discipline is a problem

The Yankees offense has gotten off to a roaring start in 2017. Boasting the third best wRC+ in baseball, the team’s ability to hit for power and get on base has made it one of the most well-rounded 1-9 lineups in the game.

A stalwart part of that lineup has been Starlin Castro. The Yankees’ second baseman has been among the American League leaders in hits all season, and Yankee fans and broadcasters have been happy to repeat that throughout the start to the season. Many people believed his start was a turning point in a career that’s stalled somewhat, launching Castro into the discussion with the other best second basemen in the AL.

The problem is, Castro’s hot streak looks like it was just that, a streak. In April, 98 PAs, he triple slashed .352/.398/.549, with a 157 wRC+. His May splits run far more in line with his career averages, .301/.328/.416, good for a 100 wRC+, exactly league-average.

Most people know that Castro’s primary weakness as a hitter is his inability to draw walks, with an overall lack of plate discipline meaning he makes far too many outs to be better than league-average. His career high in on-base percentage was .347 in his rookie year (2010), and since then he’s managed a .320 mark, though less than that in recent seasons. His 2016 OBP of .300 ranked him 67^th among qualified hitters, one slot above Jonathan Schoop.

Discipline, however, is more than just being able to take a walk. Seeing four pitches over your head, or bouncing five feet ahead of the plate, will usually result in you walking. It’s much more important for hitters to be able to recognize pitches at the edge or just outside the strike zone, and lay off.

To that end, I thought it’d be useful to look at Castro’s contact rates, and his heat maps, to better analyze the pitches he was seeing and what he was choosing to swing at.

Below is a look at Castro’s O-Swing% and overall Contact%. O-Swing% is the percentage of the pitches outside the strike zone a player swings at. I chose to use overall contact rates because a) swinging at pitches outside the strike zone is naturally going to affect your ability to make solid contact and b) there’s an opportunity cost to swinging at pitches down in the zone, especially when a batter is in a “pitcher’s count” (0-1, 1-2, etc).

You can track the peaks and valleys between these two rates throughout Castro’s entire season. Most important is the downward trend in O-Swing% to start the season, which is why Starlin got off to such a hot start. More recently, we can see the gradual uptick in O-Swing% reflecting a loss of overall contact, as Castro’s triple slash has declined.

A good partner for contact rates is a player’s heat maps: the locations of pitches he’s seeing. For most hitters, I don’t see much value in fastball heat maps, because almost every hitter hits fastballs well. What separates a Stephen Drew from a Mike Trout is often the latter’s ability to recognize breaking balls and lay off them outside the zone, and make solid contact on “hanging” breaking balls inside the zone. So with all that, Castro’s heat maps for April and May vs. breaking balls:

Starlin Castro is seeing fewer breaking balls in the zone, and pitchers have focused on delivering pitches down and away. This isn’t a shocking move, it’s nearly impossible for a batter to hit a pitch down and away with any kind of muscle. What’s concerning is this trend of pitch location, as Castro’s O-Swing% rises.

Seeing pitches well out of the zone, and still choosing to swing at them, is generally a recipe for poor offensive performance. Castro may have enough natural talent to maintain standing as a league-average hitter, but his failure to lay off bad pitches is probably the biggest factor in the delta between his potential and his performance.