The White Sox have earned their American League-best 56-36 record (through Sunday) at the plate and on the mound.
Their 5.12 runs per game rank third in the AL behind the Astros (5.35) and Blue Jays (5.21), and they have been the AL’s stingiest team with 3.77 runs allowed per game (to 3.99 for the runner-up Astros) and with a 3.55 ERA (to 3.59 for the runner-up Rays).
In the field, there’s room for improvement. By old-school fielding percentage, the Sox’ .981 ranks 13th among the AL’s 15 teams. But they fare better by numbers that capture more of the defensive picture.
With a .693 defensive-efficiency ratio, 32 points behind the Astros but two points above average, the Sox rank eighth in the AL.
Their minus-12 defensive runs saved suggests they’ve allowed 12 more runs than an average defense facing equivalent contact. That ranks 10th, with the Rays leading at plus-56.
Runs saved are compiled for each player. The Sox’ leader has been pitcher Dallas Keuchel with six runs saved, followed by outfielder Adam Engel with five runs saved in center.
On the North Side, the Cubs are struggling with a 46-47 record (through Sunday) but have a .709 defensive efficiency and are on the positive side with 24 runs saved.
The major problem with fielding percentage is that it doesn’t account for defenders’ range. Imagine two defenses face 100 balls in play, equivalent in location and velocity. One team turns 90 balls into outs but makes 10 errors. It has a .900 fielding percentage. The other makes plays on only 80 balls, turning them all into outs, makes no errors but allows 20 hits. It has a 1.000 fielding percentage.
The better defense is the one with the lower fielding percentage that turned 10 extra balls into outs.
Defensive-efficiency ratio tackles that problem by focusing on the percentage of balls in play turned into outs. The formula is 1 - (hits plus reached on error minus home runs) / (plate appearances minus walks minus strikeouts minus hit-by-pitches minus home runs).
Defensive runs saved charts every play for batted-ball location, velocity, good plays, bad plays and more. It asks whether a fielder makes more or fewer plays than an average fielder facing the same situations.
An average defender or an average defensive team would have zero runs saved.
Beyond Keuchel and Engel, Leury Garcia has taken a utility route to four runs saved — one run each at third base, shortstop, left field and right field.
For the Cubs, Javy Baez at short and Nico Hoerner at second each have five runs saved and catcher Willson Contreras and right fielder Jason Heyward have three each. So does Matt Duffy, whose runs saved all are at third, despite having played only 168 innings there.
In sum, the Sox are one of the best teams in baseball, but their defense could be tighter.