Jacob deGrom was well on his way to a third consecutive ace-level season in 2016 before an injury to the ulnar nerve in his elbow derailed it.
His condition, which occurs most commonly among those who have undergone Tommy John surgery, resulted from irritation to the scar tissue at the site of the incision, which swelled and compressed a nerve in the region. He underwent surgery on September 24, which moved the nerve to relieve the compression (the standard treatment)
DeGrom's final line for the season was strong -- a 3.04 ERA (135 ERA+) with close to a strikeout per inning and an average of just over six innings per start -- but they were all career-lows, coming after two years of quietly being one of the best pitchers in baseball.