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Mike Minor is having a terrific season, but how in the world is he leading the American League in Baseball-Reference's pitching Wins Above Replacement? Let's take a look (warning: mega-thread commencing)... 
Like with position players, WAR for pitching tries to find how many more/fewer runs someone was worth compared to league-average, then convert that into a win total. Throughout MLB history, roughly every 10 runs a player adds/subtracts, or a team scores/allows, is worth 1 win.
The two main components of Pitching WAR are simply runs allowed and innings pitched. This will get you most of the way there in figuring out a pitcher's WAR. It uses runs allowed instead of earned runs because we'll get to defense later and don't want to double count.
After this there are several adjustments made for the quality of all of your opponents' offenses, the quality of your own team's defense, your role as either a starter or reliever, and whether the ballparks you pitched in were more hitter-friendly or pitcher-friendly.
Let's use 2019 Mike Minor as an example. He’s allowed 3.41 runs per 9 IP in 174.1 IP.
The MLB average is 4.90 runs allowed per 9 IP, so Minor was better than average by 1.49 runs per 9 IP, or by 29 runs across his 174.1 IP.
The MLB average is 4.90 runs allowed per 9 IP, so Minor was better than average by 1.49 runs per 9 IP, or by 29 runs across his 174.1 IP.
Now let's make those adjustments. Minor’s average opponent scored 4.99 runs per 9 IP (after adjusting for ballpark and interleague schedules), and the MLB average was 4.90, so Minor faced lineups that were a little bit better than average.
On to defense. The Rangers are 7th-worst team in Defensive Runs Saved, so a league-average pitcher would be expected to give up 0.23 more runs per 9 IP than Minor did just based on the bad Texas D. It's the reverse for Verlander, with Houston as the 3rd-best team in DRS.
Then there's a slight adjustment for pitching role. Because relievers typically have a lower ERA than starters, SPs get a boost of about 0.23 runs and RP are docked about the same.
How about ballparks? Park Factors show how much a team's park aided or supressed scoring compared to an average one. A neutral park has a 100 Park Factor, a park that boosts offense by 5 percent has a 105 PF, one that lowers offense by 10 percent has a 90 PF, etc
Because we know how many innings each pitcher threw in each park, we can have an individual Park Factor for everyone. Jon Gray's is 117.2 (17% tougher than average thanks to Coors) and Jacob deGrom's was 91.0 (easier than usual mostly thanks to Citi).
Minor's is 110.4, a huge boost because of Arlington, and it’s the third-highest Park Factor among all MLB pitchers with 100+ IP this year, behind Rockies Jon Gray and German Marquez.
Now we can find Runs Above Average using each of these steps (opposing offense runs per 9 IP, team defense runs per 9 IP, pitching role runs per 9 IP, park factor) with this formula:
RAA = PPFp/100*(oppRA9-RA9def+RA9role)
Rolls off the tongue!
RAA = PPFp/100*(oppRA9-RA9def+RA9role)
Rolls off the tongue!
Let's apply this to Minor: 1.104 multiplier for park factor x (4.99 opp offense R/9 - -0.23 defensive support per 9 IP + 0.23 runs per 9 IP for being SP) = 6.02 RAA per 9 IP. An average pitcher would be expected to allow 6.02 runs per 9 IP under Minor's much harsher conditions.
There's that 6.02 average compared to the 3.41 runs per 9 IP that Minor actually allowed (2.61 difference).
Minor allowed 2.61 fewer runs per 9 IP than average, so across his 174.1 IP, that's 50 Runs Above Average for the season.
Minor allowed 2.61 fewer runs per 9 IP than average, so across his 174.1 IP, that's 50 Runs Above Average for the season.
Remember Minor being 29 runs better than average before our adjustments? He gets a huge 21-run boost up to 50 Runs Above Average mostly due to the ballparks he’s pitched in, Texas’s bad defense, with some credit for being a SP & slightly-tougher lineups.
There's also a multiplier for relief pitchers in high leverage. This won't effect most pitchers, but Kirby Yates & Josh Hader, for example, pitched in spots that were about twice as important on average, so they receive big boosts here.
Just like with position players, we need the difference between league average & replacement level. This is a little higher or lower based on playing time, but with 174.1 IP, Minor adds 20 runs to his 50 Runs Above Average to get 70 Runs Above Replacement.
We finally convert the 70 Runs Above Replacement into a win total, giving Minor 7.0 Wins Above Replacement, most in MLB, even higher than Verlander’s 6.7. Minor jumps him thanks to the difference between the Rangers and Astros defenses and home parks.
Like with position players, WAR separates players into tiers. 2018 had 7+ WAR Cy-level seasons by Nola/deGrom/Scherzer/Snell, 4-5 WAR star years by Cole/Severino, solid 3-4 WAR by Morton/Porcello/Tanaka, averageish 2 WAR by Teheran/Boyd, replacement-level years by Bundy/Chatwood
Just like with position players, WAR can compare pitchers in different time periods. Jacob deGrom was a 9-win pitcher in 2018, like Greg Maddux in 1995, like Ron Guidry in 1978, like Warren Spahn in 1947, like Christy Mathewson in 1905.
That's Baseball-Reference's WAR framework. Fangraphs has a their own using FIP instead of runs allowed (only based on HR, BB/HBP & K). Two different ways of trying to reach the same place. Some prefer fWAR as more indicative of the pitcher's skill, but the two are usually similar
My attempt at this pitching WAR thread certainly feels more complicated than the one for hitters, but hopefully it makes sense.
I think most fans get that pitchers can have very different situations that need to be accounted for & these measures are a good push toward that. (end)
I think most fans get that pitchers can have very different situations that need to be accounted for & these measures are a good push toward that. (end)
