In 2015, over the course of 500+ plate appearances, Jacoby Ellsbury was pretty terrible. He started the season on a synchronized offensive tear with Brett Gardner, amassing a .318 batting average and 14 stolen bases before spraining his right knee in mid-May. Upon his return, Ellsbury seemed to have forgotten how to hit. He batted .220 after the All-Star break and those numbers would have been much worse if he had not managed to hit four home runs in August. Although it would be easy to blame Ellsbury's second half collapse solely on health issues, he saw many more breaking balls in 2015 than ever before, and his failure to adjust also contributed to his prolonged slump.
According to Brooks Baseball, Ellsbury has typically seen about one breaking ball every five pitches over the length of his career.
Based on the above chart, Ellsbury had seen a slight uptick of breaking balls in recent years, but nothing significant enough to require a change in approach. After all, seeing 22% instead of 20% means an increase of only about 10-15 breaking balls over 500-600 plate appearances. Those numbers changed in 2015, when Ellsbury saw more than one breaking ball in every four pitches for the first time in his career. The increase provoked a response from Ellsbury, who pressed himself to hit more breaking balls, which resulted in an abnormally high swing percentage on breaking balls:
As the season wore on, Ellsbury seemed to press harder and harder through August, until he reached a breaking point in September:
Put in plain English, a player who had previously offered at an average of about 40% of breaking pitches decided to adjust his approach to swing at over 50% of them by August. Although his free swinging helped to contribute to the aforementioned four-homer August, it also led him to whiff much more than usual on those pitches:
The increase in whiff percentage on breaking balls contributed to the highest strikeout percentage of his career by a wide margin (17%). Amidst his best efforts to swing hard and collide with some weak sliders and hanging curveballs in a park that favors the bold lefty, Ellsbury instead cratered his ability to get on base.
Nobody can say with certainty how much of Ellsbury's 2015 performance was caused by nagging injuries. His statistics seem to indicate a frustrated offensive player, but Ellsbury did not do himself, or his teammates, any favors last season when he uncharacteristically chased breaking balls. He and the Yankees should prepare for a continuation of this trend now that opposing pitchers have found success in their tactical decision to throw them more often.