BY MARK SIMON

Kyle Schwarber had a rough re-acclimation to left field for the Chicago Cubs last year. He finished 2017 costing his team 9 runs defensively, which ranked fourth-worst among all left fielders. But in 2018, after a rough Opening Day, he’s flipped the script. His 5 Defensive Runs Saved rank fourth best at the position.

The story behind Schwarber’s improved numbers is twofold.

A more careful defender

For one, he hasn’t done the things that hurt him the most. Last season, our video tracking charged Schwarber with 29 Defensive Misplays & Errors in left field (Misplays being things that had a negative consequence, such as allowing a baserunner to reach or missing the opportunity for an out). That was a rate of one every 28 innings.

This season, Schwarber has made only 3 Misplays & Errors, a rate of one every 94 innings. If he was playing at last season’s rate, you’d expect that he’d have 10 Misplays & Errors by now.

One of the biggest issues for Schwarber last season was in his handling of the ball – he had seven misplays for mishandling the ball after a safe hit or after a catch.

Don’t run on this guy

The other key change has been in his arm rating. Schwarber has four assists that didn’t require a cutoff man, tied for most among leftfielders, all of which have come this month. Among the highlights was his throwing out Nicky DelMonico at the plate, which netted a big smile as he ran back to the dugout, and the combination of a sliding stop and strong throw to nail Francisco Lindor, who was trying to stretch a single into a double.

Throwing accuracy has thus far been good for Schwarber, who had 6 Misplays in arm-related categories (Missing the Cutoff Man and Wasted Throw After Hit or Error and Bad Throw to the Plate), but has none this season.

Those four assists are already one more than Schwarber had all of last season. As such, only four baserunners have taken an extra base (first to third or second to home on a single, first to home on a double) against him on the 18 base hits he’s fielded.

A 22 percent advance rate (lowest among all outfielders) with four unaided assists is worth four Defensive Runs Saved by itself. A 35 percent advance rate against Schwarber and three unaided assists were valued at -1 Defensive Runs Saved last season.

Early returns: positive

Though Schwarber doesn’t have a highlight reel of catches akin to some of his peers, he doesn’t need to have one to be successful. If he can take care of avoiding mistakes, his range and positioning ratings should stay steadily average.

And so long as he doesn’t fall back into old habits, word will likely get out about his arm.

In other words, if his defensive improvements match his offensive ones consistently, the Cubs should be in good shape in left field.