If you look no further than fielding percentage to evaluate defense, the Cubs look pedestrian. Their .985 fielding percentage is the same as the White Sox’, just one point above the major-league average.
Of course, everyone looks pretty much the same in team fielding percentages, which range from the Nationals’ .989 to the Brewers’ .978. But fielding percentage tells us only how good teams are at avoiding errors and tells us nothing about range, arms or positioning.
One better indicator of how good teams are at turning balls in play into outs is defensive efficiency, and that tells a different story. As listed at Baseball-Reference.com, the Cubs lead the majors with a .730 DefEff, 21 points ahead of the second-place Dodgers. The Sox (.689) are just above the major-league average (.688), and the Twins (.662) are last among the 30 teams.
The basic formula is 1 – (H-HR)/(AB-SO-HR+SH+SF). Home runs and strikeouts are subtracted because they are not balls in play and the defense is not called on to make plays. By using at-bats instead of plate appearances, walks already are excluded.
An explanation at Baseball-Reference points to a further adjustment to the numerator of 71 percent of errors. That’s the proportion of errors that result in an added runner on base, so they count alongside singles, doubles and triples.
Errors that merely advance the runner are not counted. In the case of a single plus an error that allows the runner to reach second, the ball in play is counted as not turned into an out as a result of the single, with no need to adjust for the error.
Why is that better than fielding percentage? Here’s a simple hypothetical:
Let’s say Team A is in the field for 100 balls in play. Twenty-five of the balls go for hits and the defense commits five errors, but the team turns 70 balls into outs. Its defensive efficiency is .700.
Team B is in the field for 100 identical balls in play. Thirty-five balls go for hits, but the defense is errorless, turning the other 65 into outs. Its defensive efficiency is .650.
With no errors, Team B has a 1.000 fielding percentage. But Team A has been more successful in recording outs, turning 70 of the 100 balls into outs against only 65 for Team B. The team with the lower fielding percentage is better by defensive efficiency.
That the Cubs’ defense has been a major asset is backed up by Baseball Info Solutions’ defensive runs saved. The Cubs lead the majors with 65 runs saved, followed by the Astros with 52. The major-league average is zero, and numbers are above or below average. The Sox are 11th in the American League and 25th in the majors at minus-23.
As the major-league leaders with 3.41 runs allowed per game, the Cubs have been widely praised for their pitching strength. That’s deserved, but defense plays a part in run prevention, too. And the Cubs have excelled on defense.
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