Appreciating the recent dominance of Homer Bailey’s splitter

If someone read off the best starting pitchers since the beginning of August (in terms of wOBA against), many of the names at the top wouldn’t be surprising. Jack Flaherty, Gerrit Cole, Justin Verlander, Jacob deGrom, James Paxton, and Sonny Gray all occupy the top six spots. No surprises there. Following them? That would be a surprise in Homer Bailey.

Outside of a couple serviceable seasons, Homer Bailey has not had a good big league career. Of the 179 pitchers with at least 300 innings pitched from 2014 to 2018, only Edwin Jackson and Kyle Kendrick had a higher ERA than Bailey’s mark of 5.27. In that timeframe, he accumulated only 2.7 fWAR in 377 ¹⁄₃ innings.

Bailey’s consistent struggles led to the conclusion of his stay in Cincinnati this past offseason. With little interest in services, he had to settle for a minor league deal with the Royals. He won a spot in the rotation out of Spring Training, where he proceeded to eat innings for a rebuilding Royals team at a very mediocre, but improved level (90 IP, 4.80 ERA, 4.48 FIP).

By the trade deadline, Bailey had turned himself into a viable back-end rotation option for some contending teams looking for starting depth. The Royals ultimately flipped him to the A’s for two prospects on July 14th. Pitching in Oakland, he turned it up another notch, posting a 4.21 ERA and 3.77 FIP across 12 starts. His strikeout-rate is up two percent in an A’s uniform, while his walk-rate has almost been cut in half.

The whole season for Bailey has mostly been a progressive improvement.

Baseball Savant

The month of September has produced the best version of Bailey that we’ve seen in a while. Among 125 pitchers with at least 50 batters faced this month, he ranks 12th in xwOBA and ninth in wOBA against.

Baseball Savant

A lot of Bailey’s recent success can be attributed to the dominance of his splitter. Dating back to the beginning of August, it has been one of the most effective offerings of any pitch in baseball. Out of pitchers that have ended at least 30 plate appearances with a splitter in that time, his ranks first in wOBA and xwOBA against. With it, he’s been limiting hard-contact, inducing plenty of ground balls, and producing a plethora of strikeouts (41.0 percent strikeout-rate in August, 48.0 percent strikeout-rate in September). Visually presented below, it can be clearly seen that he’s getting more whiffs on the pitch recently.

Alex Chamberlain’s Pitch Leaderboard

Examining all pitchers and all of there single offerings (minimum 200 pitches) since the beginning of August, Bailey’s splitter ranks out of 209 qualified offerings are...

• 1.62 FIP: 15th
• 0.30 xFIP: 1st
• 43.3% K%: 9th
• 0.0% BB%: 1st
• 43.3% K-BB%: 3rd

According to Alex Chamberlain’s Pitch Leaderboard, Only two other offerings in baseball during this span have a higher K-BB-rate: Dinelson Lamet’s curveball and Patrick Corbin’s slider.

Bailey is getting his splitter going at just the right time heading into the postseason. If the A’s are fortunate enough to make it past the AL Wild Card game, he’ll have a chance to play a big role in their potential playoff run, likely serving in a possible playoff rotation for them. He’s currently sitting on his best start of the season (7 IP, 3 H, 0 R, 1 BB, 11 SO against the Royals). If he can continue to keep that splitter in check, he’ll have value for the A’s during their most important part of the season.

Patrick Brennan loves to research pitchers and minor leaguers with data. You can find additional work of his at Royals Review and Royals Farm Report. You can also find him on Twitter @paintingcorner.