If you’re a regular reader of FanGraphs, and you should be, you’ll know that a project they’ve been tackling for months is finally live. The site just introduced Plus Stats for walk and strikeout rates, as well as batted ball events.
What’s a Plus Stat? It works the same way as wRC+ or ERA+. A particular performance metric is normalized where 100 represents league average, and every tick above and below represents one percentage point above or below league average. A player with a 105 BB%+ walks 5% more than league average, and a player with a 95 BB%+ walks 5% less than league average.
This is really important for two reasons. First, it helps us contextualize performance across eras. It’s no secret that baseball is becoming more and more centered around the Three True Outcomes, and that makes it difficult to compare a great pitcher from 1965 to a great pitcher in 2018. WAR is a counting stat, and since pitchers don’t throw 300 innings anymore, it’s not always the most reliable.
However, when we begin to adjust stats for the context of their time, and use a metric like adjusted strikeout rate, we can see that Gerrit Cole was 46% better than league average in 2018, and Bob Gibson was 40% better than league average in 1965. Cole struck out more than 12 batters per nine innings pitched last year and Gibson just over eight batters per nine innings pitched in 1965. When one adds the context of league-wide performance, he or she can see the two players are closer than imagined.
Second, these kind of metrics probably won’t change ideas of who the very best players are. The best hitters by these new adjusted metrics in 2018 were Mike Trout and Mookie Betts, and the best hitters of all time are Barry Bonds, Babe Ruth and Ted Williams. Where one finds real value is in identifying performance that the eye test said was one thing, and revealed to be another.
A good example of this is team-wide strikeout rates. Weren’t the Yankees far too dependent on home runs and strikeouts last year? Wouldn’t the biggest boost to their offense come down to striking out less?
The Yankees struck out only 4% more than league average last year. They were 14th in baseball when one adjusts strikeouts for the league-wide rise. As a team, they struck out at pretty much the same rate as Matt Chapman and JD Martinez. They walked 20% more, a 120 BB%+, by far the highest in the league. The Yankees gain more, relative to the league, from their offensive philosophy than they lose.
The ability to adjust crucial rate states relative to league averages is one of the most important developments in the way we evaluate baseball. It highlights the biggest changes in the game over the decades, and opens up a whole bunch of exciting avenues for analysis. I can’t wait to sink my teeth into them.