The 2020 ZiPS Projection Wrap-up, Part III: The Pitchers

The baseball season is over, but the projection season never ends, and this is always the time of the year when I look back and dissect the ZiPS projections. We’ve already checked out the hitters and the teams, leaving us the pitchers as the last bit of unfinished 2020 business. Misses are undoubtedly going to be significant in a 60-game season with little time for things to “even out,” but every mistake in the projections provides a smidgen of new information that hopefully aids in refining the work.

As with the hitters, the pitching projections avoided any systematic bias that would have given us new clues as to how certain types of pitchers fare in a mucked-up season. From age to repertoire to velocity to experience, all groups of pitchers I identified had roughly the same result: the expected reduction in overall accuracy, but no specific bias from a shortened year with a long layoff and two spring trainings.

Let’s dive into the biggest misses in ZiPS.

It seems weird for Shane Bieber, long a favorite of ZiPS, to still crush an important aspect of his 2020 projection. In terms of WAR, Bieber went from a top-10 pitcher to a top-one pitcher in the American League, besting the second-place finisher, Zack Greinke, by more than a win, amounting to a greater than 50% margin. Batters hit a mere .106 against his curve, and in more than 50% of the plate appearances that ended in a curve, the hitter struck out. He was so good that I’m happy that ZiPS missed low because it would have been preposterous for him to take such another massive step forward as a baseline!

ZiPS didn’t see Tejay Antone coming at all, and it’s rare for someone to get a 30% bump in strikeout rate upon moving from Triple-A to the majors. Antone was still a bit wild, but he’s likely to have a big jump in his 2021 projections given that ZiPS doesn’t see anything suspicious at all in the K rate. Kevin Gausman has long been one of my favorites, and it was a good sign to see him get an uptick in velocity and successfully mix in the changeup, with enough differentiation from his fosh (an old term for a splitter-change hybrid). If Gausman can have three working pitches, maybe he can survive without the breaking pitch I keep hoping he’ll develop.

Joe Musgrove is another pitcher I expect to see a big bump in the projections in 2021 and a real breakout candidate for the Pirates. 2020 saw an uptick in Musgrove’s use of his curve, which now has a 41% miss rate on swings for his career. Until 2020, the pitch was nearly an afterthought, but he used the curve this time around as a go-to weapon in all counts against lefties. The results included 10 curveball strikeouts against a whopping zero hits.

I’m highly interested in what the Rockies do with Jon Gray. While 2018’s ERA could be argued as a product of misfortune, it’s much harder to claim the same about his poor 2020 season. His velocity was down and he was shut down with a sore shoulder, which hopefully was the source of that issue. I use “hopefully” in a rather loose sense because a bum shoulder may be harder to resolve than unexplained missing velocity! Jordan Lyles was a nearly unmitigated disaster for the Rangers, leading me to wonder if Texas should just trade him back to the Brewers as that organization seems to be the only one with the ability to figure him out.

ZiPS actually thinks that Dylan Cease’s strikeout rate ought to have been higher, with him having one of the largest discrepancies between strikeout rate and the zSO that ZiPS calculates from velocity/repertoire data. There’s no such luck with Madison Bumgarner, who was down three mph from 2019. From a personal ZiPS note, I was sorry to see one of my breakout candidates before the season, Adrian Houser, take such a step backwards, but as with Bumgarner, ZiPS felt that his strikeout drop was an accurate reflection of how well he was pitching.

Deivi García’s debut didn’t involve him instantly dominating the league, but there was a lot to like about his 2020 season. It was only six starts, but he did answer some of the questions in a positive fashion, showing solid command even in his lesser outings, and showing that he could be efficient enough to work into the sixth or seventh innings. He would likely be a very valuable reliever for the Yankees in the future, but it’s even better if he continues to show the ability to start. First-strike percentage is a big predictor of walk rate for pitchers and he was well above average.

One of the stories that got less national play due to Houston’s infamous trash can scandal was just how important Framber Valdez and Cristian Javier were when it came to getting the team back into the playoff in 2020. Losing Gerrit Cole and Justin Verlander for different reasons would be difficult for any team to absorb, but this pair of young pitchers both cut down their expected walk rates in sustainable fashion. I talked more about Valdez in my rundown of ALCS Game 6, but his improved ability to hit the edges of the zone with his curve were a huge part of getting his walk rate down.

It’s not surprising to see young pitchers on this list given the error bars in that category, but it’s more surprising to see a veteran like Kenta Maeda do so well. Unlike many on this list, he didn’t have a walk problem to begin with, instead dropping nearly half of an already solid walk rate. ZiPS does see more of a regression toward the mean for Maeda than most of the rest of the list, and he had one of the largest BB vs. zBB discrepancies in baseball in 2020.

ZiPS wasn’t terribly optimistic about Robbie Ray’s walk rate coming into 2020, but he fell apart at times and unfortunately, it’s also reflected in the advanced statistics (just look at the drop in first-strike percentage!). There’s a very concerning trend in Ray’s plate discipline stats; he’s thrown fewer and fewer pitches in the zone every year, but batters aren’t any more prone to chasing these pitches. In a few years, Ray has gone from a viable Cy Young contender to a pitcher who is likely going to have to sign an incentive-laden one-year deal in free agency this winter.

The aforementioned Musgrove made this list after finishing on the positive side of the strikeout table, but ZiPS sees more improvement in his walk rate in 2021 than any other pitcher on this list, and curve-usage bumps frequently come with walk-rate bumps (I looked!). A couple pitchers here were coming off of injury/health problems the year before (Johnny Cueto, Cookie Carrasco), so I wouldn’t be overly worried about names like those too much as projection systems will always have larger errors with players in these situations, no matter how much you try and adjust for health.

Of the so-called three true outcomes, home runs tend to be the most volatile, by far, for pitchers. One of the biggest sources of projection errors are one-year bumps and drops in home runs allowed, which is why there’s a flavor of FIP that completely removes homers from the equation! For these charts, I’ve included the zHR, because when it comes to projections, this is the place where expected statistics do far better than reality in predicting the future. So unlike the strikeout and walk rates, being an over or underachiever here tends to be less “earned.”

As an example, look at Steven Matz, who had a home run rate of 9.9%, triple the 3.3% that was projected coming into the season. ZiPS still only thinks that his actual 2020 performance suggested a 3.7% HR rate, and not surprisingly, he shows up in the Statcast leaderboards as one of the largest outliers in xSLG vs. SLG and quality-of-contact wOBA vs. wOBA. Overall, there’s an eight-homer difference between Matz’s actual 2020 homers allowed and what ZiPS expected from his stats, the largest departure for any pitcher in baseball. Other pitchers to allow at least five more home runs than expected from the 2020 data are Julio Teheran, Chase Anderson, Trevor Williams, Ross Stripling, and Matthew Boyd, all players in the underachieving side.

On the flip side, ZiPS sees Germán Márquez, Justus Sheffield, Spencer Turnbull, Tyler Anderson, and Corbin Burnes as the pitchers that most overachieved from their advanced data. And not surprisingly, they also show up in the projection overachiever list.

In other words, we don’t actually know whether ZiPS or reality were “correct” quite yet. And yes, I’m aware that this is an awfully convenient position for someone with a projection system to take!

We’ve done all the components of ERA, but for historical reference, let’s finish with the overall ERA over-and-underachievers.

Next up: The 2021 ZiPS launch on 11/9!