Mason Miller Is A Month Away From History and, Arguably, the Greatest Relief Season Ever

The San Diego Padres' two-game lead for the final Wild Card spot is in no small part thanks to Mason Miller’s brilliance. He leads all qualified relievers in ERA (0.83), xERA (1.42), FIP (0.60), xFIP (1.46), WAR (3.3), K% (48.3%), K%-BB% (39.0%), and WPA (4.16). Pick a relevant statistic, and Miller is either the runaway leader or right at the top. He’s nails personified and is now only a month away from the greatest relief season in MLB history. 

Judging relief value is a bit different than position players and starters. While WAR does a great job tabulating the best starters, its context neutrality misses the mark out of the bullpen. For relievers, context is everything. You don’t bring in your closer with one out in the eighth in a one-run game with runners on first and second so he can let those inherited runners score while preserving a 0.00 ERA. No, you bring them in to put out the fire, shut the door, and put the kids to bed. 

Since individual relievers throw far fewer innings than they used to, Willie Hernandez’s 8.58 WPA in 1984 is about as untouchable a statistic as there is. Over 80 appearances and 140 innings, he posted a 1.90 ERA and brought home the Cy Young and MVP for his work—clearly, the players weren’t the only ones using questionable substances in the ‘80s. 

By WPA, Miller’s 4.16 figure only ranks 114th all-time, but that doesn’t mean he isn’t in the midst of an all-time season. His K% ranks fifth among non-2020 reliever seasons, and his FIP is staring down history.  

Among qualified relievers, Mason Miller’s 0.60 FIP is the best single-season mark ever. Which, unsurprisingly, means it’s the lowest single-season FIP (minimum 50 innings) ever recorded. Let that sink in. There have been 26,508 individual seasons and counting where a pitcher has reached 50 innings pitched, and Miller has, by one measure, been the most effective pitcher ever. 

Now, his grasp on the single most effective relief season isn’t as inevitable as he is. Craig Kimbrel’s 2012 season saw him post a 0.78 FIP, and there’s one big thing keeping Miller in the top spot: he has yet to allow a home run. FIP, short for Fielding Independent Pitching, principally takes the three things pitchers control—strikeouts, walks, and home runs—to spit out an ERA-like figure (and for FanGraphs, WAR). 

However, out of those three statistics, home run rate is by far the least predictive. This is why xFIP, which uses a league-average home run to flyball rate, is generally more predictive of future performance than FIP, especially when analyzing small samples. In terms of xFIP, which only goes back to 2002, if you remove 2020 from the sample, Miller’s 1.46 xFIP ranks sixth. 

That being said, Statcast only has Miller’s expected home runs allowed total at 0.6, so it’s not like he’s riding his luck to the top spot in history. On top of staring down FIP history, Miller has a very outside chance of claiming the top (non-2020) relief ERA season. That mark, held by Zach Britton, sits at a 0.54 ERA from 2016. Over the course of 67 innings, Britton allowed four earned runs, which means Miller, who’s at five earned runs in 54.1 innings, would have to close the season on a 29.2-inning scoreless streak to catch Britton. Even though the Padres are in the thick of a playoff race, it'd be insane to ride Miller that hard ahead of October.

When chasing history, the odds are always stacked against you. If Miller had allowed a single home run this season, his FIP would stand at 0.84, which would rank second all-time to Kimbrel’s. But that doesn’t mean he’s one home run away from being out of the race. If Miller continues to pitch as frequently and just as well based on strikeout and walk rate, but does allow a single home run, he’d end the season with a 0.80 FIP in 67.1 innings. 

That’d still be second all-time, but he could conceivably make up some lost points of FIP by racking up strikeouts at an even higher rate, or, more likely, limiting his walks. The silver lining is that Miller’s lead on adjusted FIP is a bit more secure. Adjusted FIP takes a player’s FIP compared to the league average, where 100 is league average. Miller’s mark of 14, also the best figure ever, is five points ahead of Eric Gagne’s 19 from 2003 in second. 

At the end of the day, I doubt Miller cares if he sets the single-season FIP or adjusted FIP record. The Padres are fighting for a playoff spot, and a run here or there doesn’t matter so long as they win. That being said, if for some reason you want late-game situations to be even more stressful, you can root for the Padres and Miller’s chase of history.