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Jesse Chavez’s season-changing arm slot adjustment

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Jesse Chavez says he changed his arm slot on Mother’s Day, and that appears to have altered his entire 2018 season

MLB: Texas Rangers at Houston Astros Troy Taormina-USA TODAY Sports

Jesse Chavez is now a Chicago Cub, having been traded by the Texas Rangers to the Cubs last week for A-ball lefty Tyler Thomas. The fact that Chavez, signed to a non-guaranteed deal this past offseason and seemingly a potential DFA candidate in April, was sought after by a contender, and brought back a pitching prospect, fringe though that prospect may be, is a bit remarkable.

Over at Fangraphs, David Laurila had a notes column yesterday that included some stuff on Chavez with quotes from him on a variety of topics. One thing in particular jumped out at me:

“I don’t really throw that [curveball] anymore,” Chavez said earlier this month. “I changed it to a different grip, which is now a slider, I guess. That’s because of where my arm is. I dropped my arm slot around the end of April, maybe early May. Actually, it was Mother’s Day.”

The specificity of the change got me thinking about this, and prompted me to go look at Chavez’s game logs from this season...and sure enough, Chavez did pitch on Mother’s Day this year — May 13, 2018.

Prior to that outing, Chavez had a 5.48 ERA, allowing opponents to slash .330/.361/.560 against him, with a .391 BABIP.

On May 13, Chavez threw 3 shutout innings, fanning 4 during a 6-1 loss to Houston. From May 13 until the trade, Chavez had a 2.53 ERA, with a .233/.276/.400 slash line and a .250 BABIP.

That’s a pretty significant improvement.

Now, one can argue that maybe this is simply BABIP-luck driven, and not reflective of improved performance by Chavez. If we drill down a little further, from the start of the season through May 9 — his last pre-Mother’s Day outing — Chavez had a 49.3% hard hit rate against a 13.0% soft hit rate, with a 4.75 FIP, a 23.7% K rate and a 5.1% walk rate. From May 13 on, he has allowed a 31.2% hard hit rate against a 20.2% soft hit rate, with a 3.84 FIP, a 20.5% K rate and a 4.8% walk rate.

So the strikeouts and walks aren’t much different, but hitters aren’t hitting the ball as hard, it appears, with the result being he’s allowing fewer home runs and fewer balls in play to go for hits.

Chavez likely isn’t going to maintain the post-arm-slot-change 2.53 ERA he’s had, but he’s also probably going to be much better than he was in the first month-plus of the season. And it is interesting that a change that he identified seems to dovetail with a significant change in fortune.