Austin Slater, the Best Role Player in Baseball

I’m gonna start this one with a hot take: superstars can be boring. Before the pitchforks come out, let me explain myself. I love it just as much as everyone else when Aaron Judge obliterates second-deck homers, Jacob deGrom throws triple digits with ease, or Shohei Ohtani, well, does both. But the way star players contribute to their teams is quite predictable. Provided he’s healthy, Mike Trout’s name will be somewhere on the top third of the lineup card with a little number eight on the position column 155 times a year. Manager Phil Nevin doesn’t have to make any difficult decisions about when or where to start him.

But for most fans, the base unit of their baseball viewing experience is a team, rather than an individual player. The average Hennepin County resident would probably say they’re a Twins fan rather than characterize themselves as a Carlos Correa or Byron Buxton supporter. Often times, the same principle is true of baseball analysis. Sure, we write a lot about single players, but individuals don’t play in a vacuum. My favorite part of every free-agent signing to write is about how a new player fits into the roster they’ve just joined, and WAR, possibly the most referenced metric on this site, is literally an estimation of how much a team victories a given player adds. Heck, we had 58 people comment on a piece about projected team standings even before the majority of free agents had signed.

So, back to my original thesis. The game’s best players are incredibly awe-inspiring in what they can do on the field, but we don’t get to think about the role in which they’re best used, because that role is just “all the time”. Earlier this week, I wrote about Dylan Moore, who signed a three-year extension with Seattle. He’s not the most exciting player to write about as an individual; he doesn’t have monster exit velocities or dominate the contact leaderboards. What he does do, though, is patch about ten holes the Mariners have or may have in the future due to platoon issues, defensive limitations, or injuries. Seattle’s front office realized that a single non-starting player could be the solution to many team-specific problems and gave Moore a small pile of money to remain in the Pacific Northwest for the foreseeable future. Moore was fun to write and think about because of the specific ways in which he complements the team around him, and I like this type of analysis because it’s much more unique to each individual player and their team.

It’s time we get to the subject of this piece. In my Moore article, I found that nearly half of his plate appearances came against left-handed pitching, which placed fourth among righty hitters. The man who ranked first? Austin Slater of the Giants. An up/down bench outfielder for his first three years in the league, he earned a full-time roster spot in 2020 and has made the most of it despite his non-starting role, amassing 4.6 WAR in 735 plate appearances (3.8 WAR/600 PA). While he’s appeared in at least 125 games in each of the last two seasons, he’s only made 116 starts. But starting the game on the bench hasn’t seemed to affect his performance, with a 118 wRC+ during that time.

One way in which Slater has generated value as a reserve has been through pinch-hitting. While the sample sizes are small, he has among the best numbers of any regular pinch-hitter in MLB history:

It’s important to keep in mind the small sample sizes here, but a more likely and explainable cause of his success is the quality of situations that the Giants have put him in. As previously mentioned, Slater was deployed against left-handed pitching more than any other right-handed hitter, largely because he would often enter the game once a starting pitcher was replaced by a southpaw reliever. Indeed, 79 of his 92 pinch-hit opportunities over the past two seasons have been against lefties; he has an OBP nearing .500 in those plate appearances. Leo Morgenstern wrote about the ludicrous frequency with which the Giants have used pinch-hitters compared to other teams in the DH era, and one of his key findings was their unrivaled aggression in going to their bench in the fifth and sixth innings. Slater was often the first man up to relieve left-handed outfielders Joc Pederson and Luis González against a lefty, as both had exaggerated platoon splits.

Slater’s usage, especially as an early-inning pinch-hitter, seems rather unorthodox. Often times, pinch-hitters enter late in games to win an individual matchup and because their spot in the lineup is unlikely to come up again. Clearly, the Giants had no issue with Slater batting multiple times after entering in the fifth or sixth, and why would they? He was actually above-average against right-handed pitching last season after being significantly worse in years prior, though it remains to be seen whether or not he can maintain that in future seasons. And even if he isn’t a stellar hitter in less favorable matchups, he certainly provided defensive relief over Pederson and González, who combined for -14 RAA. And he’s done all of this despite the fact that pinch-hitting is really difficult. Sitting around for a couple hours before stepping into the box for the first time seems far more difficult than getting loose in the field to warm up, and studies have estimated pinch-hitters suffer a 20-point reduction in wOBA compared to their norms for this reason. But Slater has actually gained over 110 points of wOBA in his pinch-hit slots, a trend which Leo observed in his piece applied to San Francisco’s pinch-hitters as a whole.

Slater has always been a patient hitter, with a career walk rate north of 10% and a .345 OBP. But arguably the biggest key to his offensive success has been his .343 BABIP, and I think this is largely sustainable. He has a very flat swing path designed to punish flat four-seam fastballs with carry, which have become the meta of pitching in the era of advanced pitch data. As a result, over half of his batted balls were grounders, but he sprays them all over the infield and has above-average home-to-first times, making him less susceptible to crafty defensive positioning. Hitting line drives is probably the best way to boost your BABIP, and Slater’s liner rate sits in the 90th percentile, both because his swing is geared to hit them and because his disciplined approach prevents him from making weak contact on bad pitches.

But what’s perhaps most interesting is what happens when Slater hits a fly ball. It doesn’t occur often — just under a quarter of the time — but he makes the most of these chances. While fly balls, on average, do the most damage due to the potential for homers, they’re also free outs if hit too high. MVP finalist Nolan Arenado had 88 batted balls with a launch angle of 50 degrees or higher, which produced a lone hit and 87 outs; many other big-time power hitters have a rather large number of pop-outs and wasted fly balls. Slater, on the other hand, had just five such batted balls all season. That’s why, despite middling exit velocities and just seven homers all season, he had a .599 wOBA and .439 BAcon on fly balls and popups, dwarfing the league averages of .371 and .255.

On defense, Slater has experience all over the outfield, with at least 600 career innings at each spot and numerous occasions where he played multiple outfield positions in the same game. In 2022, he spent the bulk of his time in center after Steven Duggar’s offensive performance regressed, leading to an early-season release. Defensive metrics were extremely divided on his abilities out there, though. While DRS considered him atrocious with a mark of -9 (-22 DRS per 1350 innings) and UZR had a similarly negative view, Statcast credited him with +1 RAA. According to the components of Statcast’s jump data, Slater was a bit slow reacting to balls hit his direction but made up for it with solid route efficiency and an average top speed of over 28 feet per second, which ranked in the 74th percentile. When considering all factors, he actually covered 0.2 feet more ground than the average fielder, which tied him with Gold Glove winner Myles Straw and electric rookie Julio Rodríguez. While the metrics disagree, I think Slater is at least not hurting his pitching staff when roaming the vast center field of Oracle Park and is solidly above average in the corners, something that UZR and DRS agree about as well.

Much has been written about teams like the Rays and the Giants of the past few years who have found a way to construct a team greater than the sum of its parts. Understanding how teams make the most of their available personnel is probably my favorite part about studying and writing about baseball. But these teams are made up of players, many of whom are put into unfamiliar roles as non-everyday starters. Slater has proven himself to be a natural in his role, both as a multipositional defender and a hitter who can come in off the bench and mash no matter the situation. And while we love to watch the Judges and Trouts of the world do seemingly impossible things day in and day out, sometimes it’s equally as impressive to watch someone like Slater dependably do their job, even if they don’t know what that job is until the middle of the game.