Schifman: A new metric for skill shown on batted balls

From Gerald Schifman at The Hardball Times on July 24, 2018:

Last year, Twins fans were treated to the emergence of uber-talent Byron Buxton. The former No. 2 overall draft pick regularly appeared on defensive highlight reels and showed an elite ability to run the bases. With his sprint speed, ranked by MLB Advanced Media (MLBAM) as being baseball’s best, Buxton was able to turn ordinary batted balls into close plays and possible hits. One example is this ball in play against the Astros last year.


Shortstop Carlos Correa made a great play here, diving to keep the ball on the infield and jumping quickly to his feet to unleash a strong, accurate throw to first. Even with that, Buxton’s tremendous speed turned this batted ball into a hit. The play is exciting yet predictable, given all we know about Buxton’s athletic talent. There was a strong chance of a single off the bat, an outcome which tends to be worth 0.9 runs towards the offensive team’s cause.

Yet MLBAM’s xwOBA, which measures the expected value of a batted ball based on Statcast data, pegs Buxton’s BIP as being worth just 0.392 runs—less than half of a single’s typical value. The metric seems to be missing something here, which is perhaps unsurprising given its fairly simple formulation: xwOBA takes a batted ball’s raw exit velocity and launch angle combination, and assesses its actual value, consulting nearby neighbors where necessary to expand the sample size.

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Originally published: July 24, 2018. Last Updated: July 24, 2018.