Monday Morning Sabermetrics: oStr% and zBall%

Higher oStr% is better, lower zBall% is better.

In the Major League world of automated strike zones, there is so much data we have available to us to break down the defensive prowess of big league catchers. This is an additional variable that we must adjust for when evaluating pitchers: the ability of their battery mate to present the pitch to the umpire in a fashion so that rarely will strikes be called balls, and even balls will occasionally be called strikes. All else held constant, a pitcher who has the best receiving catcher in baseball will post much better unadjusted numbers than the one with the worst receiving catcher in baseball.

Many times we look back and think, if only we had that close 3-2 pitch called a strike instead of a ball, the hitter would have been out and those multiple runs would not have gone on to score. Good receiving catchers can be incredibly valuable to a team and prevent scores of opposing runs over the course of a 162-game season. To measure the catcher’s ability to receive, we turn to two metrics, oStr% and zBall%. oStr% is the percent of pitches outside the strike zone called strikes by the umpire, while zBall% is the percent of pitches within the strike zone called balls. The formula for each is below:

oStr% = (Strikes called on pitches outside the strike zone/Total pitches taken outside the strike zone)

zBall% = (Balls called on pitches within the strike zone/Total pitches taken within the strike zone)


Based on the above formulas, one can deduce that the optimal catcher has the highest oStr% and the lowest zBall% in the league. The current leader in oStr% (minimum 3000-pitch sample size) is Miguel Montero of the Chicago Cubs, buying an impressive 10.6 percent of pitches outside the strike zone for Cubs pitchers. At the bottom of the barrel in oStr% is three-time gold glover Salvador Perez of the defending world champion Kansas City Royals, buying only 5.9 percent of such pitches. Counterintuitive, right? The automated strike zone is robust; perhaps Perez will not earn a fourth gold glove this season.

The lowest zBall% in baseball belongs to Yasmani Grandal of the Los Angeles Dodgers. Just 9.5 percent of strikes Dodger pitchers throw to Grandal are not called as such. In contrast, the highest zBall% in baseball, owned by Dioner Navarro of the centrifugal Chicago White Sox, is 19.1 percent. This means that almost one out of every five White Sox strikes thrown to Navarro are called balls even though they find the zone.

We can take into account oStr% and zBall% and the sample size of each catcher to arrive at the number of total strike calls a catcher has more or less ‘bought’ for his pitching staff. Divide that by games caught to arrive at Calls per Game, and, by extension, the number of runs the catcher has saved defensively over an average catcher. The link to the complete chart of this, on StatCorner, is at the end of this article.

Buster Posey (SFG) currently leads all catchers in Calls (132) and RAA (17.5), while Montero leads in Calls per Game (2.35).


Up Next: We wrap up the summer next Sunday, July 31st, with additional baseball ideas and in-game strategies used to optimize a team’s run expectancies and win expectancies over the long haul. Derived from thousands of games of data throughout baseball history, this is what we know.


Previous Sunday Morning Sabermetrics Articles:

June 5th: Pythagorean W-L:


June 12th: Wins Above Replacement:


June 19th: OBP/SLG/OPS/OPS+


June 26th: BABIP, ISO, and wOBA


July 1st: SecA, RC, and wRC+


July 10th: ERA+, RA9, and FIP


July 17th: Game Score for Pitchers:



Link to StatCorner table of 2016 MLB catchers oStr% and zBall%:



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