After opting for a patchwork solution at second base since Robinson Cano's departure two years ago, the Yankees finally decided to acquire a hopefully longterm solution when they traded 2015 bullpen and rotation stalwart Adam Warren to the Cubs for Starlin Castro. In doing so, they bet on their bullpen and minor league arms to pick up the slack. They also bet that Castro, whose contract runs through 2019, would maintain his steady defense at a relatively new position, and the offensive gains he made in the second half of last season. Those gains were at least in part due to his willingness to offer at offspeed pitches, so Castro should maintain his willingness to sit on changeups.
During the offseason, the media has made it a habit of emphasizing the fact that Castro has already made three All-Star appearances even though he just turned 26. Despite that impressive accomplishment, Castro's career has been viewed as a disappointment so far. He followed up his excellent age 21 season with a moderately successful 2012, during which he was voted to his second All-Star appearance but was also caught stealing a major league leading 13 times and was statistically average at the plate. In 2013 Castro hit rock bottom with a wRC+ of 73 over 700 plate appearances, which contributed to an overall profile barely exceeding replacement level. Luckily Castro would bounce back with an excellent 2014. However, his season would end in early September due to an injury suffered while sliding into home plate. 2015 was marked by offensive inconsistency and a position change.
With an up and down track record at the plate, one identifiable theme seems to be Castro's relationship with changeups. Since 2010 Castro has maintained a somewhat steady approach to fastballs and breaking balls, but seems to continuously change his mind about the appeal of the changeup:
Year after year Castro has never made a radical adjustment to his willingness to swing at fastballs. His most discerning season was 2014 with a 43.99% swing rate while his least was 2011 at 49.24%. While those two numbers seem relatively far apart, Castro has never varied more than 4% in consecutive years. Castro has not been nearly as consistent in his approach to breaking balls, but his variance has not been radical. Yes, last season saw a steep jump in Castro's willingness to swing at breaking pitches, but prior to 2015 he had settled in between 45 and 51% (last season he offered at 54%).
The most obvious trend in the above chart is that Castro can't make up his mind about changeups. Throughout most of his career he has been lukewarm in his willingness to swing at offspeed pitches, hovering around a 49-52% offer rate. During 2012 and 2014, however, Castro seemingly decided to offer at greater than 60% of the offspeed pitches he saw. On the surface, that willingness seems to be a contributing factor to two of Castro's three above average offensive seasons. His other above average offensive season, 2011, did not feature quite as elevated an offspeed offer rate, but in breaking down that season on a monthly basis we can glean a similar pattern:
Above are Castro's 2011 monthly splits. Below are his 2011 offer rates broken down monthly as well.
Referencing the above offer rate chart, you'll see that his offspeed offer rate was significantly elevated in June, August and September, which coincides with the most successful offensive stretches of that season. He was most reticent to swing during April, May, and July. The only two months during which Castro struggled that season were May and July.
Applying a similar strategy to Castro's up and down 2015, a similar pattern emerges:
Castro began 2015 with a hot April before cratering into the earth during May, June and July. He was actually benched by manager Joe Maddon in early August before he was converted into a second baseman. Following his conversion in mid-August, Castro broke out offensively and had an OPS over 1.000 during the month of September. Referencing the above offer rate chart, one may notice that his offensive breakout coincided with Castro's decision to start swinging at about three of every four changeups. Thanks at least in part to his approach adjustment, Castro was a vital piece of Chicago's offense down the stretch last season.
Overall, statistics seem to indicate that good things happen when Starlin Castro swings at changeups. In a young career marked by inconsistency, Castro's most accomplished offensive stretches have come when he has attacked offspeed pitching, while some of his lowest points have coincided with reticence. Joe Girardi and hitting coach Alan Cockrell should keep this strategy in mind should Castro begin to waver in 2016.