What is Ben Heller’s upside?

You’ve heard me say this before, but I’ll say it again: The Yankees’ bullpen has more unknowns than sure things—literally. Three spots are filled in the form of Dellin Betances, Aroldis Chapman, and Tyler Clippard, while five other places are up for grabs between an assortment of unproven relievers and starters who will miss the rotation. I can’t yet say this is a bad bullpen, but that’s mostly because I have no clue who will end up pitching out of said bullpen.

Luckily, the Yankees do have quite a few interesting, if not volatile, candidates for their relief corps. One of which is the subject of this article—Ben Heller—who was acquired last year as a secondary piece in the Andrew Miller blockbuster. If you had the stomach to stick with the Yankees in their final month of 2016, you may be familiar with Heller’s work. If you directed your attention elsewhere for September, you didn’t miss much. In the 25-year-old’s first taste of the big leagues, he threw seven shaky innings, giving up five runs on 11 hits and four walks (along with three home runs) while striking out six. The performance was in stark contrast to his minor-league numbers, which have been stellar since he was drafted in the 22^nd round by the Indians in 2013. Last season, Heller had a 1.69 ERA between Double-A and Triple-A, striking out 55 in 48 innings as a reliever.

It’s hard to accurately evaluate a player like Heller, though, because success in the minors doesn’t often translate to the big leagues and his time with the Yankees was far too short to draw meaningful conclusions from. Armed with a fastball that lives in the high nineties and a slider that slides enough to play off the heater, it’s unsurprising that the reliever thrived in the minor leagues, but this tells us little about what to expect in extended big league time. Just ask every other reliever that the Yankees gave a shot last season—they were all lights out below the MLB, but struggled once on the Yankees.

So, if we can’t use the minor leagues and we can’t use the major leagues to draw a conclusion about Heller, we’ll have to go with some old-fashioned scouting. The most obvious takeaway from Heller’s time with the Yankees last season was his outstanding fastball, which averaged 95.5 mph and frequently stretched up to 97. Interestingly, Heller was clocked in at 96-98 mph by evaluators earlier in the season (Baseball America mentions he’s also hit triple digits), so the righty may have tired some down the stretch. If that’s the case, we could expect a small increase in the elite velocity he showcased in the big leagues.

There’s more to this fastball than just velocity, though, which is what makes it a potential plus-plus pitch. Minor league reports mentioned “heavy armside run” on the pitch, and PITCHf/x numbers agreed…and then some. His fastball showed an average of 9.71 inches of horizontal movement, breaking ‘in’ to right-handed batters. For context, this was 2^nd best in baseball last season among right handed pitchers, behind only Joe Smith.

While the velocity or arm-side run alone don’t make a fastball effective, combining them makes for a rare combination of potential dominance—it isn’t easy to find a hard fastball with excellent movement (I’m talking to you, Nathan Eovaldi and Michael Pineda). While the immediate results off the fastball were nothing special last season, that could be attributed to fatigue and, of course, the fact that it was his first look at the big leagues after just 30.2 innings in Triple-A. Given the velocity and movement from the fastball, there’s a good chance it can be poison on hitters in future seasons.

Heller’s secondary pitch is a slider, and although it’s nothing special, it doesn’t have to be given the outstanding fastball. Provided the pitch is at least average, Heller can be an above average middle reliever, and if the pitch proves better than average, there is tremendous upside for him. The slider lacks the same elite velocity his heater possesses, and the movement is also unremarkable, but it has enough depth to play off the fastball and make hitters think twice before sitting on the four-seamer.

While relievers are incredibly weird—enough to quickly render this whole article irrelevant—Heller’s showing last year was very promising, despite the disappointing results. He may not be an elite, late innings reliever to pair with Betances and Chapman, but there’s enough here to profile as a reliable middle reliever with setup man upside. Heller may not realize either role early next season, but the raw stuff is enough that he could very well make the bullpen out of spring training and emerge as one of their better bullpen pieces in due time.