No, quality of opponent is not why Shane Bieber faltered

The highly-anticipated Shane Bieber-Gerrit Cole pitching matchup was down the tubes rather quickly. Four pitches into Tuesday evening, it was 2-0 New York. A first-pitch four-seam fastball from Bieber to Aaron Judge caught too much of the plate and was deposited into the empty right-center field seats. You just can’t leave a fastball right here:

That pretty much set the tone for the rest of the night. Bieber — the runaway favorite to win the American League Cy Young award, in addition to being very much in contention to win the American League MVP — unraveled. He only lasted 4 ²⁄₃ innings, his shortest start of the season, and allowed seven runs, tying his career-high. It very clearly wasn’t the postseason debut that Bieber could have wanted, and considering the nature of the Wild Card Series, one could say it basically represented the end of the Indians’ 2020 title hopes.

Explanations for Bieber’s poor outing ran wild, with some suggesting that Bieber’s lack of quality opponents throughout the regular season allowed him to put up video game-esque results that didn’t actually represent his true talent. Bieber did have a historic season, even if it was only in 12 starts: He pitched to a 1.63 ERA over 77 ¹⁄₃ innings. When comparing his numbers to the best 12-start stretches of all-time, that ERA figure ranks in the 97th percentile. The underlying number were sterling as well: A 41.1 percent strikeout rate, 7.1 percent walk rate, and 2.07 FIP all confirmed Bieber’s regular season dominance.

But was it just the result of pitching against weaker offenses? Since regular season schedules were regional this year, Bieber only faced lineups from the Brewers, Pirates, Reds, Royals, Tigers, Twins, and White Sox. Only two of those teams — the White Sox (114 wRC+, 6th-best in the major) and Twins (101, 16th) — had above-average offenses across the board. The other five teams were all in the bottom-third of the majors in adjusted offensive output.

This argument that Bieber (and the rest of the Central pitchers) faced weaker lineups has been very relevant in the Cy Young debate, particularly in the National League. In an attempt to make his own case for the Senior Circuit’s Cy Young, Trevor Bauer has claimed that the cause-and-effect relationship for the Central teams having poor offense is unclear: Is the Central region bad at hitting only because they have good pitching? Or, is it indeed bad hitting with pitching that has capitalized?

It’s a fair point in defense of his argument (and it might also aid in my proposal for regional, rather than league, awards), but at least in the case of Bieber, it doesn’t seem to matter all that much. Bieber faced a total of 79 different hitters this season, from Jorge Polanco, whom he faced 10 times, to Derek Hill, Adam Frazier, and Kyle Farmer, whom he all faced just once. If you sum the seasonal numbers from those 79 different batters, you do find that Bieber’s average opponent this season was worse than league-average wOBA. However, if you properly weigh how often he faced each of these hitters — by saying that Polanco’s stats should be 10 times more relevant than Hill’s, since Bieber faced Polanco 10 times more — we find that his average opponent was only slightly worse than the league-average wOBA:

In fairness, in both the equal and properly weighted averages, this data does include plate appearances versus Bieber, so his opponents’ wOBA would be suppressed further due to facing him. Thus, it’s not too much of a stretch to say that the average batter Bieber faced this season wasn’t too much worse (if at all) than the league-average batter overall. Pretty interesting, indeed.

Let’s compare that to the lineup Bieber faced on Tuesday night. Bieber faced the 1 through 7 hitters on the Yankees three times and the 8 and 9 hitters just twice, so there’s not a huge difference between the equal-weighted and the plate appearance-weighted data, but here is all of it nonetheless:

Clearly, the Yankees have a good offense, but this doesn’t necessarily “prove” anything as far as Bieber’s implosion.

To support this, we can consider just how many more runs Bieber was “expected” to allow given the wOBA differences in the lineup he faced on Tuesday versus the hitters he had faced throughout the regular season. The difference in appearance-weighted wOBA — again, this takes into account that Bieber faced DJ LeMahieu three times but Brett Gardner only twice, for example — between the Yankees’ lineup and Bieber’s 2020 regular season opponents is 51 points. But what does this really mean? This means that, for every 23 batters Bieber faces in the Yankees’ Tuesday lineup, he would be expected to allow one more run than usual. So, based solely on his new opponent, Bieber should’ve pitched something like seven innings of two-run ball instead of the seven innings of one-run ball we had become accustomed to over the past two months. In no way does quality of opponent explain Bieber’s lousy outing.

To further support this, here’s some anecdotal evidence: On Tuesday, Central pitchers Kenta Maeda (five innings, zero runs) and Lucas Giolito (seven innings, one run) both looked just as good as they did during the regular season, even facing different opponents.

Ultimately, Shane Bieber had an incredible season, and one poor postseason performance should not invalidate that. So much of baseball can be attributed to randomness — a guy not having his best stuff on any given day happens all the time — and that just seems to be the case here. Unfortunately for Bieber and for Cleveland, the implosion just happened to come the worst possible time.

Devan Fink is a sophomore at Dartmouth College and a Contributor at Beyond The Box Score. Previous work of his can be found at FanGraphs and his own personal blog, Cover Those Bases. You can follow him on Twitter @DevanFink.