Eric Campbell hit .197 last year with a 77 wRC+, and the fact that he made the team out of spring training has made some—or all—Mets fans scratch their heads.
Sandy Alderson said last July that he likes Campbell's peripheral statistics. The Mets have way more access to these types of peripheral statistics than the public does, but here are some that are available that Alderson is probably referencing.
One big one is exit velocity. The harder the ball is hit, the more likely it goes for a hit. This data is taken from the great Daren Willman, who runs MLBAM's analytics department:
Just looking at exit velocity doesn't take into account trajectory, which is also extremely important. The public doesn't have access to launch angles yet, which would be the preferred objective method. Instead, trajectories are subjectively classified into 3 groups: ground balls, line drives and fly balls.
Statcast, which debuted last year, measures the velocity of the ball as it comes off a hitter's bat. According to statcast, the league hit .670 on line drives that left the bat at 90+ mph. Campbell only hit .385, significantly below what the norm for line drives at those speeds would be. This particular peripheral statistic may indicate some bad luck, something that would normalize if Campbell kept hitting the ball the same way over a longer period of time. That could be something the Mets are considering with Campbell.
However, the problem with just looking at exit velocity on line drives is that not all line drives with the same exit velocity are created equal. A 95 mph liner with ferocious topspin is probably going to dive into the ground and away from gloves more aggressively than a flat 95 mph line drive without much spin in either direction. The same can be said for fly balls: the more backspin a fly ball has, the more it's probably going to carry away from a fielder's glove. Batted ball spin rates aren't public yet, but maybe Campbell's batted ball spin rates make his well hit liners hang in the air longer for fielders to catch them, or make it easier for fielders to get a read on and position themselves well to catch it.
Steve Schreiber also made a great observation on Friday evening after Campbell lined out to the third baseman in the Mets final spring training game:
That was hit hard but I wonder if his "bad luck" has anything to do with the angle at which he hits the ball. Doesn't get a lot of lift.— PastAPeeingHarvey (@_mistermet) April 1, 2016
Maybe there's something inherent in Campbell's skill set that contributes to what could be viewed as bad luck at first glance, such as the aforementioned flat batted ball spin caused by the nature of his swing.
I don't want to overlook hit placement, either, the old "hit it where they ain't." Perhaps Campbell's hit placement tool just isn't very good, and he's prone to hitting well hit balls right at fielders.
Either way, whether Campbell had a lot of rancid luck on batted balls hit right at fielders or if he is just more prone to what may appear to be "bad luck" by factors inherent in his skills, the Mets like what their peripherals on him suggest, and that's probably why he's on the 2016 roster out of the gate despite very poor production last season.