Starlin Castro’s poor plate discipline is more complicated than it looks

With the recent Aroldis Chapman trade, an influx of exciting former Cubs has bolstered the Yankees’ farm system. But for former Chicago phenom Starlin Castro, a change in scenery has not worked out as planned. His .694 OPS is below league average, even for second base, a traditionally light-hitting position. Early in the season, he showcased the pop in his bat that everyone knew about. Unfortunately, he has fallen back into his old habits, which include chasing pitches outside the zone and hitting too many grounders.

Last month, Ben Diamond noted Castro’s inability to lay off breaking balls in the dirt for Baseball Prospectus. He also noted that Castro is actually aware of the fact that he struggles with breaking balls below the knees, and still can’t seem to stop swinging at them. His findings are easily reinforced by Castro’s platoon splits, as he has hit lefties better than righties throughout his career. He has also done worse against sliders than any other pitch, according to Fangraphs’ Pitch Value metric.

It would make sense that Castro struggles on pitches down in the zone because of his inability to lay off breaking balls. But in reality, the inverse might be true. Castro might in fact be failing to lay off sliders in the dirt because he is actually a very good low-ball hitter. Take a look at his zone profile from 2015 to the present, with his batting averages and slugging percentages shown.

Pitches in the lower third of the strike zone have been Castro’s bread and butter over the last 1.5 seasons, even though he has been a below average hitter during that timeframe. It is possible that Castro has an even harder time laying off breaking balls in the dirt because he knows that he does the bulk of his damage on pitches in the lower part of the strike zone.

In addition to his low-ball hitting tendencies, it looks like Castro also favors pitches on the middle to inside part of the plate. Unfortunately, that hasn’t stopped him from taking the occasional lunging hack at pitches down and away.

No hitter can avoid chasing sliders in the dirt 100% of the time. For someone like Castro, who thrives on pitches down in the zone, laying off low breaking balls is probably even harder than usual. When thrown correctly, a slider will look like a low fastball out of the pitcher’s hand, which would be right in Castro’s wheelhouse.

But not all low-ball hitters are doomed to a life of poor plate discipline. Over in Los Angeles, the Angels have a prolific low-ball hitter of their own in Mike Trout. Looking at his swing pattern, compared to Castro’s, an interesting trend emerges:

Trout will chase the occasional pitch below the strike zone, as is expected. But when he does go after pitches below his knees, they tend to be on the middle to inner part of the plate. He actually tends to avoid outside pitches altogether.

It is possible that avoiding pitches on a certain side of the plate is easier than trying to do so by height. Fellow AL West superstar Jose Altuve has recently improved his plate discipline, mainly by not swinging at as many inside pitches:

Not swinging at pitches below the strike zone is clearly a difficult task for Castro, and we really can’t blame him. But if he can learn to lay off pitches that miss outside, it might improve his plate discipline just enough for him to become an effective hitter again. Right handed pitchers often try to throw their sliders down and away to right handed hitters, so by focusing on the inside to middle of the plate, Castro could be able to trick himself into avoiding them.

Castro’s chronic plate discipline issues might also provide insight as to how hitters develop. While analyzing certain hitters, we often find ourselves wondering what would happen if a certain player improved his plate discipline, but it rarely ever happens. In the future, teams might consider evaluating a hitter’s potential to improve his plate discipline based on where he struggles the most.

For now, the Yankees will have to hope Castro can turn things around. There is always the hope that he can do something about his 50.3% groundball rate, even if he doesn’t stop swinging at pitches outside the strike zone. Either way, Castro will need to make some kind of adjustment in order to live up to his star potential once again.

Data is courtesy of Fangraphs and Brooks Baseball.