Looking back at the strange evolution of CC Sabathia's slider

Once upon a time, CC Sabathia used to dominate hitters while really only using three pitches. Armed with a fastball that could touch the upper 90's, a slider, and a changeup, the big man used to make fools of hitters on a regular basis. To say he went on a tear after being traded from the Cleveland Indians to the Milwaukee Brewers in 2008 doesn't do his post-trade performance justice. Needless to say, there were a lot of things to like about the pitcher the Yankees signed before the 2009 season.

As a Yankee, Sabathia's knee problems, weight, velocity dip, and choice of breakfast have all come under intense scrutiny. But a couple of changes have flown under the radar, relatively speaking. His release point has dropped over the last few years, something a talent evaluator attributed to his weight loss, suggesting that it might have messed with his mechanics.

One of the things that may or may not have been affected by his changing mechanics has been his slider, according to Pitch F/X at least. He's only lost a couple of ticks on his slider, but the horizontal movement on the pitch has been all over the place:

Note: As a lefty, a lower value on the horizontal movement scale means more sweeping action. Andrew Miller had -4.8 inches of horizontal movement last year.

Some of the change in Sabathia's slider movement could be because of his changing release point. Generally, pitchers with a lower arm slot will have more armside run on their fastballs, so something similar could be true of sliders. But if Sabathia's arm slot has been dropping, it would not explain how he suddenly regained three inches of lateral movement in 2015.

Here's the kicker: for all the talk of sliders being a "platoon pitch," throwing sliders to right handed hitters was always an important part of Sabathia's game. He has always used his changeup almost exclusively for righties, but he still mixed his breaking ball in as well. Even in 2013, the year fans really started to worry about his fastball velocity, Sabathia threw his slider to righties 22.4% of the time, holding them to a .194 average and a .358 slugging percentage. Even more fascinating is the fact that he wasn't scared of leaving it in the zone, according to this heatmap from Baseball Savant:

To summarize, Sabathia lost a bunch of movement on his slider without adding velocity and still managed to succeed, while throwing it in the strike zone to righties. In 2015, he found that sweeping action once again. In another strange twist, righties crushed the pitch, putting up a .349 average and .603 slugging percentage. Getting more movement on his slider should have been a good thing, but Sabathia paid dearly for it last year.

At this point, it's tough to tell what kind of pitch CC will have in spring training. If he inexplicably returns to about -2 inches of horizontal movement, Sabathia's woes against righties might just go away, since his slider in 2013 served him well. If not, he might consider taking a page out of Andrew Miller's book and trying to bury it in on the hands of right handed hitters more often. Either way, it is important that Sabathia is aware of what his slider is looking like in Spring Training and that he forms a plan around it.

Data is courtesy of Brooks Baseball and Baseball Savant.