Is Luis Severino having the greatest pitching season in Yankees’ history?

When does something start to feel historic? It can be tough to pin down. At what point during Barry Bonds’ 73-homer season did fans realize they might be seeing a new home run record? During what summer month did Marlins fans last year realize Giancarlo Stanton could be making a run at 60 home runs? When, in 2018, will fans ask if we’re seeing the best pitching season in history by a Yankee?

Luis Severino is 17 starts into his 2018 campaign. In his most recent start, this week against the Phillies, Severino fired seven more shutout innings. It was the fifth time this year he didn’t allow a run. He’s allowed more than three runs only once all season.

I would posit that now, halfway through the year, is a fair time to start wondering about where this season from Severino will rank in Yankees’ lore. The Yankees have the most decorated history of any team in American sports, and what Severino is doing now puts him on pace to top virtually every pitcher who has ever put on the uniform.

The numbers speak for themselves. Severino has tossed 111.2 innings. He has struck out 132 batters, and walked only 26. He has allowed 27 runs, good for a 2.10 ERA. For those wondering how the team has fared when Severino has started, well, his record is 12-2, and the team is 15-2 in his starts.

Those are just the raw stats. To really put things into a historical context, it’s helpful to adjust for league and park effects. Severino has an ERA- of 50, which means his ERA is 50 percentage points better than the league average. Likewise, his FIP- is 52.

That FIP- would be the best by a Yankees pitcher in a qualified season after the turn of the 20th century, according to FanGraphs. His ERA- would be second-best behind only Ron Guidry, who posted a 47 ERA- in 1978.

On a rate basis, Severino’s season has basically been the best ever by a Yankee so far. Volume matters too, however. Obviously, Severino can’t match the volume of prior years in a half season, but we can use the pace he’s on to see how he would stack up overall if he kept up his current performance.

Let’s start by using Baseball Reference’s version of WAR. The Yankees have played 79 games, and Severino has 4.4 rWAR. That puts him on pace for almost precisely 9.0 rWAR.

9.0 rWAR would put Severino fifth all time in Yankees’ history, behind Russ Ford (11.3), Jack Chesbro (10.4), Guidry (9.6), and Lefty Gomez (9.3). Take note, though, that Ford’s and Chesbro’s seasons happened in the early 1900’s, when starters routinely took the ball and didn’t hand it over until the game was done. Chesbro accumulated his massive WAR total over 51 starts. Ford threw 299.2 innings in posting over 11 WAR. We shouldn’t simply discard their accomplishments because they happened a century ago, but we should take into account the era in which they occurred when comparing them to current players.

Really, in terms of modern Yankees’ history, Guidry’s season is the one Severino is competing with. This is borne out if we switch to FanGraphs’ calculation of WAR. Severino has 4.2 fWAR on the year, on pace for about 8.8 fWAR, which would place him second all time, behind Guidry’s 1978 (9.1 fWAR).

After adjusting for context, it really looks like it comes down to Severino and Guidry, if Severino can keep this up. In that 1978 campaign, Guidry threw 273 innings with a 1.74 ERA, during a year in which the average pitcher had an ERA in the mid-threes. He struck out 248 and walked 72. He won the Cy Young award, and finished second in AL MVP voting.

At this rate, Severino would finish with about 230 innings, and 270 strikeouts. He has a chance to win over 20 games and the Cy Young award. What would be more impressive? Guidry’s higher volume season, with a lower ERA in a more pitcher-friendly era? Or Severino, with a slightly higher level of dominance at a slightly lower volume?

If Severino keeps up this pace, the WAR totals will say it’s a tossup, and I tend to agree. Regardless, Severino has truly been historically good so far, and his 2018 has a legitimate shot of going down as the best ever in New York. Anything can happen, as regression in performance and injury are always risks with pitchers. Making history is hard: that’s why it’s historic. But Severino has as good a chance as any in recent memory to post one of the finest seasons in the Yankees’ storied history.