The WPA Argument
For those of you unfamiliar with WPA, or Win Probability Added, it measures what a single event in a baseball game does to change the likelihood of a team winning, given all circumstances. For example, a grand slam does more for your team when down three with two outs in the ninth, then when up by five in the seventh.
Each individual play a batter makes can swing the game probability, each outcome a different variant of change. The ninth inning example above offers a 91.64 percent change in win probability, while the humdrum fifth inning salami only changes the outcome by 46.58 percent.
Each change of probability is reduced from a percentage to a decimal value, so if a player hits that walk off grand slam in the ninth inning, he would be credited with .916 WPA (derived from that 91.64 percent swing).
Players do not hit walk off grand slams every day (looking at you, Steve Pearce), and are much more likely to go 0-4 while hitting into a few double plays—and that’ll bring your numbers down significantly. Most players WPA game logs have consecutive daily values of 0.05, -0.02, 0.01, -0.09, etc.
The Major League qualified leader is Bryce Harper with 4.43 WPA over 102 games, improving his team’s chances of winning by about 4.3 percent each game on average.
Tim Beckham, in his 6 games of glory, has .37 WPA. That’s improving the Orioles chances of winning by 5.3 percent each game. That doesn’t seem like much, but consider Bryce Harpers league leading WPA as a comparison.
Beckham is improving the chances of an Orioles win every night significantly more than the best player not named Mike Trout, in all of baseball. (Trout is still the best at everything, with a WPA over Harpers, at 4.35. He’s only played in only 68 games, so he doesn’t even qualify. His rate, an astonishing 6.4 percent per game).