James Paxton’s new changeup

Yesterday, James Paxton threw the very first pitches of the Mariners’ 2016 season. Sure, they might have been in a meaningless exhibition game before the not-as-meaningless exhibition games begin, but it was organized baseball between two different ball clubs. Paxton is fighting to stake his claim on the fifth spot in the rotation and where he ends up might be one of the most compelling storylines of the spring. Luckily for the Mariners, it looks like he’s ready to take a big leap forward.

It may be a cliché, but Paxton entered camp this year in excellent shape. Gone was the dadgut, replaced by the determination to shake the injury-prone label that’s haunted him his entire career. His figure wasn’t the only thing that had changed during the offseason. On Tuesday, Bob Dutton reported that Paxton had worked on improving his pitch arsenal during his time in the Arizona Fall League. The numerous finger injuries he suffered last year prevented him from throwing his big curveball. Instead, he focused on his other two pitches:

"We were working on fastball location, a high fastball and my changeup. I think it helped me a lot. My fastball command, I think, got better over that time. My high fastball. And the change-up, it was my only off-speed pitch, so I had to throw it. Being forced to throw it made it that much better. It made me get comfortable with it. That was a big plus for me."

A few months ago on FanGraphs, Jeff Sullivan made an excellent case for Paxton’s high fastball. In that article, Sullivan compared the amount of backspin Paxton gets on his fastball to similar pitchers and found that he rarely elevates the pitch. Instead of generating whiffs with his fastball, he’s generating weak contact lower in the strike zone. That's not necessarily a bad thing—weak grounders are a positive outcome—but it doesn't leverage the raw stuff and potential he possesses. These two heat maps illustrate the point perfectly:

Here’s Paxton’s pitch location heat map from his start yesterday:

So, it looks like he still working on his fastball location. A more granular look reveals a little bit more confidence. He generated three whiffs yesterday, all off his fastball, and two of them were in the upper half of the strike zone. It was just one start and just 34 pitches so we shouldn't be jumping to any conclusions. His velocity clearly wasn't as high as it is normally and he's probably still getting into the routine of pitching regularly again. Still, his fastball location should be monitored throughout the spring.

As for his changeup, Paxton threw just three of them yesterday. Thankfully, the Arizona Fall League is played in PITCHf/x equipped stadiums. A query of that data shows some big changes to his cambio. The following table compares the velocity and movement of his changeup prior to his AFL stint and during his AFL stint.

Paxton’s changeup lost three ticks off its average velocity, widening the gap between it and his fastball to ten miles per hour. But the biggest change was the amount of "rise" he generated with the revamped pitch. He was already generating a good amount of vertical movement on the pitch—his changeup had the 7^th highest vertical movement among lefties who threw at least 100 changeups last year—but he’s taken it to an extreme now. In fact, in the PITCHf/x era, there have been just two pitchers who have generated double digit vertical movement on their changeups: Clayton Kershaw and Eric Milton. The amount of vertical movement Paxton is generating is more than an inch more than these two pitchers. With such a big outlier, we have to start thinking about calibration errors. Even if the PITCHf/x data is a bit wonky, we can probably assume that Paxton has increased the amount of rise on his changeup, we’re just not sure by how much. Until we get more and better data or some good video footage, we'll just have to live with the tantalizing promise we may have glimpsed in the AFL data.

Common wisdom says an effective changeup will mimic the pitcher’s fastball in all but velocity. Batters will be hard pressed to differentiate the two pitches if they move similarly. By generating more rise on his changeup, Paxton is adapting the pitch to look more like his fastball. Perhaps that’s one reason behind the spike in his strikeout rate in the AFL. Monitoring the shape of this pitch during spring training will tell us a lot about his potential to breakout this season. Of course his health will always be the key to his success, but a revamped pitch arsenal could help him show why he’s the leading candidate to earn the fifth spot in the rotation.