By Mark Simon

One of the storylines to follow for new Phillies outfielder Bryce Harper this season will be how he fares defensively. Harper’s defense cost the Nationals 26 runs last season, tied with new teammate Rhys Hoskins for second-worst in the majors. Harper struggled defensively in both right field, where he’ll likely play for the Phillies, and center field, where he played just under 500 innings for the Nationals in 2018.

Harper’s performance last season was about more than his inability to turn batted balls into outs at a high rate. Harper also cost his team with his troubles deterring baserunner advancement. Harper had -6 Outfield Arm Runs Saved last season, by far the worst total of his career (he saved five runs in the previous two seasons combined). He cost the Nationals five of those six runs in right field. From that position, Harper did not record any baserunner “kills” (a BIS term for throwing out a runner trying to advance without the help of a cutoff man). From 2015 to 2017, Harper totaled 16 assists in right field without using a cutoff man.

Baseball Info Solutions Video Scouts chart defensive plays, categorizing them as “Good Fielding Plays” and “Defensive Misplays & Errors.” Harper had five Defensive Misplays & Errors that were grouped as “Wasted Throw After Hit/Error” that allowed a runner to take an extra base. The only players with more were Billy Hamilton and Ender Inciarte, who had seven.

Harper is not the only star player to have a poor Outfield Arm Runs Saved total. In fact, one of the trailers in that stat is 2018 NL MVP Christian Yelich. Yelich cost his team seven runs with his arm, four in left field and three in right. Yelich has had this problem wherever he’s played. In 2017, he played the entire season in center field and cost the Marlins six runs with his arm. He did save four runs for the Brewers overall, making up for his arm issues with good Range & Positioning numbers.

Another big free agent signee, A.J. Pollock, brings a lot of skill to center field with the Dodgers. However, his arm cost the Diamondbacks six runs at that position in 2018. Pollock allowed 71 percent of baserunners to take an extra base on a base hit (go first-to-third or second-to-home on a single, or first-to-home on a double). That was the highest advancement rate allowed by center fielders last season. In a smaller sample, Harper allowed a 67 percent advancement rate.

Though Harper, Yelich, and Pollock are extremely valuable position players, they would be even more valuable if they can improve upon this aspect of their games in 2019.

Another standout, Cubs left fielder Kyle Schwarber, tied Twins left fielder Eddie Rosario for second, one run behind Judge. Also worth spotlighting is Yelich’s teammate, Brewers center fielder Lorenzo Cain, who went from costing the Royals six runs with his arm in 2017 to saving his team five runs with it in an outstanding 2018 campaign.Though the focus is largely on Harper here, it doesn’t seem right to end this piece without referencing the leaders in this stat. One of them was one of the game’s biggest stars, Aaron Judge. Judge saved eight runs with his arm, the most of any outfielder in MLB.