Getting Joe Musgrove to the Next Level

Joe Musgrove was a pretty ordinary pitcher in 2018, with a 103 ERA- and an 89 FIP- according to FanGraphs. He once again battled through injuries on the way to a career-high 115.1 innings, and he had more woes to deal with in the offseason by undergoing abdomen surgery. He doesn’t particularly stand out in Pittsburgh’s rotation, as he doesn’t have the track record or high transaction cost of Chris Archer, he doesn’t have the easy-to-root-for, feel-good story of cancer survivor Jameson Taillon, and he doesn’t have the intriguing out-of-nowhere 2018 performance of Trevor Williams. He is rather ordinary among starting pitchers. Even when I ran a query of starters with similar 2018 statistics, I got back a list of some good-but-perhaps-underwhelming hurlers. Look here:

Nothing against these pitchers (especially Miles Mikolas, who had a good but perhaps unsustainable 2018 when looking at xFIP and SIERA, which he at least parlayed into a big contract extension), but these aren’t names that come to mind first when you think of the top pitchers in the league, and Garrett Richards isn’t usually on the mound to move up into that category in the first place.

This isn’t a great endorsement for Musgrove, so why am I interested in him? I drafted Musgrove in both of my fantasy baseball drafts earlier this month, prioritizing him over the other names in the above table. I did this based on the work of Nick Pollack, founder of the great website Pitcher List and contributor to FanGraphs, who has talked up Musgrove for awhile now. On the now- famous Top 100 Starting Pitcher Rankings featured on Pitcher List, Musgrove ranks 44th, ahead of the previously mentioned Archer (54), Alex Wood (69), Marco Gonzales (77), and other notable pitchers such as Cole Hamels (47), Jon Lester (48), and Dallas Keuchel (73). There must be an explanation for this.

On Musgrove’s FanGraphs player page, Pollack writes that his 4.7% walk rate in 2018 was no fluke and that he features an offering of secondary pitches that could easily push his strikeout rate to a much better 25%. I always have an interest in low-walk-rate starting pitchers, but one with an above-average strikeout rate? Now I’m interested.

I decided to get into the numbers myself and see which starting pitchers are comparable to Musgrove if he kept the same numbers as last season, but instead with a 25% strikeout rate. Using the same query I did in the previous table, I added that requirement, while also looking for a K-BB% less than or equal to 20.3% (25% K-rate minus Musgrove’s 2018 4.7% BB-rate). Here are the results:

Richards’ limited sample is featured again, but overall this looks like a better tier of pitcher than in the previous table. While not featuring the truly elite tier of pitchers, this group had an average 2018 fWAR of 3.12 (excluding Richards), a number that would rank 23rd among starting pitchers from 2018.

This all sounds nice, but how exactly do we get Joe Musgrove to a 25% strikeout rate? I decided to look at Musgrove’s Statcast data courtesy of Baseball Savant to get a better idea of his pitches. Here is a table of his 2018 Statcast pitch data, with some important figures highlighted in bold:

The key takeaway from this table is that Musgrove’s two biggest strikeout pitches, the slider and changeup, not only generate dominant strikeout and whiff rates, but also that according to xwOBA (expected weighted-on base-average), the pitches underperformed. He only threw these pitches about a third of the time combined, and his best strikeout pitch (the changeup) less than 15% of the time. It appears from this table that by changing up the pitch allocation and throwing the offspeed and breaking ball more than his platter of fastballs, turning into a true three-pitch pitcher, Musgrove could get his overall strikeout rate up. While just throwing these pitches more often doesn’t guarantee an increased strikeout rate, it does look like it’s worth a shot.

The last area I wanted to look at was how Musgrove’s 2018 progressed and if his performances were better with a pitch mix featuring his slider and changeup more. First, here is a graph showing Musgrove’s 2018 cumulative average slider percentage, changeup percentage, and strikeout rate:

From this, you can see that up until game 12, Musgrove’s strikeout rate was very volatile, jumping around in no real pattern. From the lowest strikeout point in game 12, which took place August 6th, he began to use both his slider and changeup at an increased rate, and his strikeout rate also rose at a consistent rate, increasing as his slider and changeup use rose. From here, I decided to look at his game logs, looking both at performance level stats like FIP and xFIP as well as his pitch mix to look at if he got better results from August 6th onwards. Here are the top seven 2018 game logs, sorted by xFIP:

Five out of seven of Musgrove’s best performances by xFIP occurred past August 6th, when he began to use his slider and changeup at the highest rates of the season. This is a sign perhaps that he should keep using those pitches more often. Let’s look a bit further into these five games by checking out the pitch mix in those contests:

One thing I should note is that FanGraphs considers Musgrove having a curveball along with a slider, whereas Statcast only recognizes a slider, so you can consider the slider percentage column to be the slider column plus the curveball column, as the percentage of curveballs is small enough that it doesn’t skew the overall point of the table. Anyway, looking at this data, you can see that during these best starts by xFIP, Musgrove usually featured a larger mix of his non-fastball pitches and threw his changeup more often than his season average each time except once, and he threw his slider more than his season average each time while throwing less fastballs as a whole, moving away from the cutter in the final three starts in favor of increased changeup use. This combination of good results with a different pitch mix looks to be a good sign for his performance that he hopefully takes into 2019 to at some point become a big part of the Pirates rotation.

While Joe Musgrove may seem underwhelming at first glance, going a bit deeper shows that he may have figured something out down the stretch of 2018 and will look to carry that forward into 2019. Musgrove started his year with two perfect innings out of the bullpen against the Reds on March 31, as he may be getting up to speed after his offseason surgery. However, I do believe that if Musgrove continues to switch up his pitch mix, he can push himself into a better tier of pitcher and establish himself as a solid, well-above-average starting pitcher for the Pirates, and we may even look back on this season as his breakout year.