How this change is helping Roddery Muñoz fix his home run issue

Buying a ticket in the outfield seats for the first several starts of Roddery Muñoz’s major league career was a great investment. The 24-year-old right-hander was serving up souvenirs left and right.

Called up due to the smattering of injuries to the Miami Marlins starting rotation, Muñoz allowed a staggering 15 home runs in his first eight starts (40.1 IP). During that period from April 20 to June 29, Munoz’s home run/fly ball ratio of 26.3 percent was worst in the league among all pitchers with at least 35 innings pitched, as was his HR/9 of 3.35.

Acquired last offseason in exchange for cash considerations and lacking previous MLB experience, the expectations for Muñoz were low to begin with. Still, it was hard to understand why somebody with his high quality of pure stuff was so easy for hitters to square up.

What went wrong?

The first thing that jumped out while researching for this article was Muñoz’s four-seam fastball. Using it relatively equally with his cutter and sinker as his most-used pitches, he allowed significantly more home runs on the fastball than on the latter two pitches.

During his first eight starts, Muñoz had a negative-5.5 run value on the four-seamer, according to Pitch Info from FanGraphs, which was tied for tenth-worst in the league among pitchers with at least 40 innings pitched. His sinker, by comparison, was a relatively-better negative-2.2 while his cutter was grading out at negative-0.8.

Judging by the heat maps and his velocity, there is nothing that stands out about why his fastball was so feeble. He doesn’t live over the plate any more than other pitchers of higher caliber do, and his average fastball velocity of 95.2 miles per hour ranks in the top third of pitchers this year. Even FanGraphs has his Stuff+ graded as a 98, with 100 being league average.

How did he fix the issue?

During Muñoz's last start on August 10, Bally Sports Florida Interviewed fellow starting pitcher Sandy Alcantara and asked him about the rookie's growth.

Alcantara, who has taken on the role of coach and mentor while he recovers from Tommy John surgery this season, said on the broadcast that Muñoz had been tipping his pitches. When he was first called up, the 6’2" Dominican would hold his glove around his belly button when he came set for the pitch out of the windup and hold his glove slightly off his body. That made it easier for opposing hitters to see him adjusting his pitch grip and anticipate what he'd be throwing.

Alcantara, along with Edward Cabrera and pitching coach Mel Stottlemyre Jr., helped fix this issue by having Muñoz lower his glove to his belt and hold it against his body. Here's the comparison between Muñoz's loanDepot park debut on May 1 and his most recent outing:

It’s unclear when they discovered this issue, but in watching tape, it seems he began fixing his stance during his relief appearance against the Chicago White Sox on July 5 and was more consistent with it in his following start against the Houston Astros on July 11. Perhaps not coincidentally, that game against the White Sox began a set of three consecutive appearances over 15 ⅔ innings in which he did not allow a home run.

While still not a reliable starter by any means, Muñoz has considerably improved the underlying stats mentioned above. Since July 5, he has pitched in seven games, one of them being a relief appearance, for 34 ⅓ innings. His fastball run value has gotten marginally better, at negative-4.4 runs, while his sinker is at plus-2.0 and his cutter is plus-0.3. His FIP has gone down by two full runs, from 7.69 before July 5 to 5.62 after that date.

This subtle change is showing up in the more standard numbers as well. In his last seven appearances, he has allowed six home runs (one for every 26 batters faced). In his first eight games, he allowed 15 home runs (one for every 11.66 batters faced). His slugging percentage allowed has also dipped from .569 to .482.

With none of the injured Marlins starters ready for game action anytime soon, expect Muñoz to get ample time to hammer down this fix.