Brennan Boesch and the O-Swing% Difference


This winter, you could have put together a lengthy links roundup every week comprised solely of pundits lauding Brennan Boesch as primed for a breakout season. Popular RotoGraphs author Jeff Zimmerman believed Boesch had 20-homer, 100-run potential batting ahead of Miguel Cabrera and Prince Fielder, cornerstones of a perceived powerhouse Detroit Tigers lineup. According to Buster Olney on Twitter, David Ortiz was known to think Boesch “headed for a monster year.” Reports from spring training indicated positive signs of a strong and healthy slugger and as Grapefruit League play wound down, he belted three home runs in the span four days to bring his spring total to six, one behind three men—including Albert Pujols—tied for the major league lead.

Boesch was also first on former major league general manager Jim Bowden’s list of “seven players poised to erupt” for Insiders in February. The word from Bowden on Boesch was to not be surprised if the Santa Monica slugger hit 25-30 home runs. The catch, in the words of Bowden, was this realization of Boesch’s raw power would come “as the 26-year-old learns to become more disciplined at the plate and waits for the one pitch he can drive.” Bowden also lamented Boesch’s propensity to “inconsistency” and the “occasional long swing.”

But through more than a month of real baseball, Boesch’s plate approach has changed none. The “occasional long swing” Bowden mentioned is more frequent than episodic. Boesch has walked little—twice in 115 plate appearances—and hit for a .205 average. After being given every opportunity to succeed, he has finally lost his prime spot, high in the Tigers’ batting order.

The problem is not hard to discern if you watch one or two of his at bats and it’s nothing new; Boesch has an O-Swing% (the percentage of pitches outside the strike zone he’s waved at) of 38.8. That rate trails only Andy Dirks (who, coincidentally, has taken over batting second for the time being) on the Detroit roster, but Dirks finds success anyway thanks to a 90.2 O-Contact% (the percentage of swings at pitches outside the zone which the bat finds) while Boesch’s O-Contact% sits far lower at 68.2. The 38.8 O-Swing% for Boesch is actually below his career average of 39.4.

A poor O-Swing% might be the worst quality in a number two hitter, whose main task is to get on base. Naturally, O-Swing% is directly related to poor batting average and walk rates, two statistics of which upkeep is necessary for a decent on-base percentage. Splitting major league baseball by a cutoff of a 38.8 O-Swing% (Boesch’s), the contrast is huge: the 110 players who have made at least one plate appearance and whose O-Swing% is equal or greater than Boesch’s have thus far combined for a 4.04% walk rate and a .225 batting average. Those figures for the rest of the league (before games on May 7th) are 8.81% and .252.

Boesch is neither being selective within the zone, currently holding a team-high 73.9 Z-Swing%. Only 14 qualified players across baseball have swung at a higher percentage of total pitches than Boesch’s 53.4%.

(Plate discipline numbers in this article are from Baseball Info Solutions via FanGraphs.)

Terrible plate discipline has hindered Boesch, a player otherwise teeming with potential, for his whole career and is presumably a significant factor behind his glaring streakiness. Unless he can learn to control his bat like Vladimir Guerrero, Boesch will need to be more selective at the plate. If he doesn’t—and fast—that breakout will never come.