When the San Diego Padres acquired right-hander Joe Musgrove over the winter, as part of a three-team and seven-player trade that also involved the Pittsburgh Pirates and New York Mets, the widely held expectation was that they would change him. Though already established as an above-average starter, Musgrove's arsenal appeared unoptimized in a way that made him low-hanging fruit for a savvy pitching coach. (That the Pirates had seen other pitchers leave and flourish in recent years, such as Gerrit Cole and Tyler Glasnow, probably aided the perception of Musgrove as "fixable.")

It's early, but so far things have gone according to plan. Musgrove, altered pitch mix and all, opened the season with 16 consecutive shutout innings, including a no-hitter (and near perfect game) vs. the Texas Rangers. Through four starts, he's sporting a 1.04 ERA and a 12.33 strikeout-to-walk ratio. He's allowed 11 hits and three walks in 26 innings, all the while recording 37 strikeouts and a 70 percent strike rate. In a rotation alongside Yu Darvish and Blake Snell, two former Cy Young Award winners, it's been Musgrove who has looked like San Diego's ace.

What's behind Musgrove's excellent start? Let's take a look at three contributing factors.

1. More cutters

As teased above, Musgrove has altered how he uses his pitches. The single greatest difference is the emphasis he's placed on his cutter. Musgrove is throwing 19 additional cutters per 100 pitches this season, bumping his usage from 6.4 percent in 2020 to 24.8 percent in 2021. The cutter is now his second most used offering, behind his slider.

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You might suspect that Musgrove's cutter is a relatively new addition to his arsenal, and that he didn't feel comfortable incorporating it before this season. That isn't the case. He's thrown a cutter dating back to 2017; he just never used it as more than a show-me offering with the exception of the 2018 season. Musgrove threw 15 percent cutters during that campaign, but went away from it after the opposition hit .296 off it.

You might also suspect that Musgrove's cutter was a secret darling in his arsenal. Again, that's not necessarily the case. He threw only 43 of them last season, with opponents batting .429 against it with a .571 slugging percentage. It should be noted that Musgrove's cutter missed far more bats in 2020 than it had in the past, and that he's since altered the spin and movement profile of the pitch.

The answer to "why did the Padres instruct Musgrove to throw more cutters?" might have less to do with what they saw in his cutter and more to do with what they didn't see in his four-seam fastball.

2. Fewer fastballs

As mentioned above, the biggest difference in Musgrove's pitch mix is that he's throwing more cutters. Well, the second biggest difference has been the de-prioritizing of his fastball. Musgrove is throwing 14 fewer four-seamers per 100 pitches, reducing his usage from a repertoire-leading 26.9 percent to a fourth-place 13.4 percent. 

It's easier to understand Musgrove's fastball migration from a results perspective. Opponents hit over .300 against the heater the last two seasons, and in three of the past four seasons overall. Even this year, reduced usage and all, it's been his most-hit pitch. During Musgrove's most recent start, Monday night against the Milwaukee Brewers, he recorded 13 strikeouts. Not a single one of those came on a four-seam fastball.

What's interesting is Musgrove had taken to elevating his fastball more often last season. While that would seem like a good idea based on his spin rates, his fastball lacks the kind of profile that is normally found in heaters that dominate up. For example, Musgrove had a higher fastball spin rate in 2020 than Tampa Bay Rays reliever Pete Fairbanks, but Fairbanks' fastball had a more efficient spin and moved on an axis that created a truer optical illusion for backspin fastballs than Musgrove's. Add in how the 6-foot-5 Musgrove is a short strider, thus reducing the perceived velocity of his pitches, and you have the framework for an explanation on his fastball's shortcomings. 

Granted, this is all a bit in the weeds for most, so let's end with a tried-and-true concept.

3. Weak competition

You can pitch only to the opponents on your schedule, but have you seen who Musgrove has faced so far? He opened the season against the Arizona Diamondbacks, and has since taken his turn against the Rangers, the Pirates, and the Brewers. Here's how those offenses rank according to FanGraphs' wRC+ metric, which adjusts for ballpark

  • Diamondbacks: 19th
  • Rangers: 23rd
  • Pirates: 17th
  • Brewers: 29th

Admittedly, there's a bit of a chicken-or-egg situation going on here because of the small sample sizes -- the Rangers would certainly rank higher if Musgrove hadn't no-hit them -- but you can make the case he's yet to face an above-average offense. That doesn't mean he's going to wilt whenever he sees a good lineup for the first time; it is, however, an important piece of context in explaining his dominant April.

If you are waiting for Musgrove to face a high-quality lineup before buying in, then you won't have to wait for much longer. His next start is scheduled to come on Saturday against the Los Angeles Dodgers, or the team with the National League's best offense.