Bryan Mitchell's 2015 struggles: An investigation

Entering the 2015 season, Bryan Mitchell was ranked as the number 12 prospect in the Yankees' minor league system by Baseball America and as the number 14 prospect according to MLB.com. He has two plus pitches: a fastball that tops out at 97 mph with movement and a power curve that is a groundball-generating machine.

Mitchell performed well in his brief cup of coffee in the 2014 season, posting a 2.45 ERA (3.22 FIP) in 11 total innings pitched, and he continued this success upon initially being called up to the majors in June 2015. Mitchell pitched to a 1.59 ERA in 5.2 innings in June (1.55 FIP) and to a 4.91 ERA in 3.2 innings in July (with a much lower 3.13 FIP).

However, Mitchell's 2015 success was short-lived. After gaining Girardi's trust through his impressive pitching in the two months following his call up, Mitchell pitched 14 innings in August. During this month, he pitched to a 4.50 ERA, which, while not all that worse than his ERA in June, was accompanied by worse peripherals such as a 4.21 FIP. Things grew even worse in September, in which Mitchell threw 6.1 innings to a 15.63 ERA (9.77 FIP). The question is, what caused Mitchell's dramatic shift in performance level?

Mitchell's advanced statistics shed some light on the culprit of his pitching woes. Hitters had a BABIP of .313 against Mitchell in June and an even lower BABIP of .273 against him in July. Come August, opposing offenses had a .364 BABIP, and they had an atrocious .429 BABIP against Mitchell in September. Luck plays a significant role in a pitcher's BABIP allowed; Mitchell's almost identical hard hit rates in the first half of the season (29.6%) and the second half of the season (31.9%) indicate that some of his BABIP woes could have definitely been the result of bad luck.

It is also possible that bad luck hurt Mitchell in the second half of the season in terms of home runs allowed. He did not surrender any home runs in 9.1 innings in the first half of the season, but he allowed 20% HR/FB and 40% HR/FB in August and September, respectively. The aforementioned similarity between Mitchell's first and second half hard hit rates shows that perhaps poor luck played a role in his allowing more home runs in the second half of the season.

Luck clearly played a role in Mitchell's poor performance in August and September. However, it is probably not bad luck, but rather Mitchell's inability to control his pitches that caused his terrible pitching in the second half. Mitchell has always had command issues. In Triple-A in 2015, Mitchell had a 4.44 BB/9 and an 11.7% BB rate, and MLB.com's scouting report only graded Mitchell's command a 40 on the 20-80 scale.

Upon being called up to the majors in 2015, Mitchell was able to keep his walk rates down; he posted a 1.93 BB/9 and 5.1% BB in the first half of the season. However, his command significantly regressed in the second half, in which he had a BB/9 of 6.20 and a walk rate of 13.5% (ouch). To put all of this in context, FanGraphs classifies a 2.9 BB/9 and 7.7% BB rate as "average." It classifies "awful" as posting a 4.0 BB/9 and a 9.0% walk rate. Clearly, Mitchell's second half stats in 2015 would be classified as far beyond awful.

Two caveats must be taken into consideration with all these numbers. First, Mitchell only pitched 29.2 innings in the major leagues in 2015; all statistics are thus subject to a small sample size bias, and Mitchell's splits might not carry much meaning.

Second, on August 17^th, Mitchell was struck in the face by a 103 MPH line drive off the bat of Eduardo Nunez. While he had three August appearances prior to this game, this traumatic moment did occur around the middle of the season. Though I don't want to get into amateur sports psychology, it would hardly be surprising for this incident to get into his head; other pitchers struck on line drives like Brandon McCarthy and Bryce Florie have admitted that it can take some time to overcome. Following the injury, Mitchell had a 10.38 BB/9 and an enormous walk rate of 20%.

Walks killed any chance Mitchell had of pitching well in the second half of 2015. His scary injury could have caused anxiety of locating the ball over the plate. Hopefully, the offseason will give Mitchell time to distance himself from the trauma he encountered in 2015 and will infuse him the confidence to throw strikes in the upcoming season. The 2016 Yankees could really use first half Bryan Mitchell on their roster, especially following the trade of long reliever Adam Warren.