ST. LOUIS -- With the acquisition of Dexter Fowler, the Cardinals secured a new leadoff option as well as a fresh clubhouse voice. The club also instantly improved its defense.
The latter point may not seem so obvious, as advanced defensive metrics reveal that Fowler has been, at best, an average center fielder during his career. In fact, the numbers suggest he just peaked defensively in 2016 -- at age 30.
Fowler projects to cover about as much ground in center as Randal Grichuk did a year ago. Though Grichuk posted a higher Defensive Runs Saved figure (seven) than Fowler (one), Statcast™ data shows that their center-field range charts nearly overlap. These catch-rate charts illustrate how similar the two were in center in 2016:

To understand the illustration, it's important to know that catch rate is based on a fielder's distance from the ball, the ball's hang time, and the performance of all Major League fielders at that position. The above chart plots batted balls with a catch rate of 25-75 percent, which is the range where fielders can distinguish themselves at the position. (For this exercise, we're exluding the 0-25 percent range because those are overwhelmingly hits, and the 75-100 percent range, which are overwhelmingly outs.)
But while the Cardinals' center-field defense may not have been upgraded with this acquisition, their left-field coverage will be. By signing Fowler, the Cardinals can slide Grichuk to left, where he projects to offer a significant defensive upgrade.
"I don't want to sit here and say Fowler's defense isn't good," general manager John Mozeliak said. "I think Fowler plays to about average. But I do think moving Grichuk over automatically makes our outfield stronger because Grichuk, Fowler and [Stephen] Piscotty, to us, seems good."

Last season, Cardinals left fielders finished 26th in the Majors with a -10 DRS while Matt Holliday and Brandon Moss, neither of whom will return in 2017, handled the bulk of the work. Grichuk, in contrast, profiles as an above-average defender there.
In order to ensure an uptick in overall outfield coverage, the Cardinals intend to build off the positioning changes that helped Fowler in the field in 2016. After finishing with -12 DRS in his first season with the Cubs, Fowler was approached in Spring Training with data that supported the idea of positioning himself further back in center. He applied the suggestion with success.
Statcast™ data shows that Fowler started at an average of 321 feet back in 2016. That represented an increase of 17 feet. Coupled with his sharp DRS improvement, this data asserts that Fowler didn't necessarily become a better player last season, but rather that he was put into position to perform better.
"I was getting crushed with the defense," Fowler said. "They said I was a bad outfielder, and I kind of took offense to that. So I just moved back a few steps and played where everybody else was playing. It took some getting used to. I felt like I was playing no doubles all the time. ... But I think I'm doing all right."
Fowler's defensive position was not only five feet farther back than the average Major League center fielder, but it was also an average of nine feet deeper than St. Louis' center fielders, according to Statcast™.
The Cardinals, who studied Fowler's change of positioning before courting him this offseason, intend to keep a keen eye on it in hopes that 2016 can be just the start of Fowler's defensive renaissance.
"Positioning is critical," Mozeliak said. "That's something we have to stay on top of. He's a really bright guy, too. He's probably someone who is going to help with that."