Could Aaron Heilman Make For a Decent Rotation Option in Arizona?

With C.J. Wilson effectively moving from the bullpen to the rotation last year, 2011 has brought a number of other attempted reliever-to-starter conversions. Detroit is looking at Phil Coke as a starter, and the Rangers are giving Neftali Feliz a look in the rotation.

Longtime reliever Aaron Heilman has long stated that he wants to start, despite not starting a game since 2005 and never starting more than 13 in a season in the big leagues.

Arizona seems willing to indulge him, however, at least on a temporary basis. The righthander has made two starts this spring, and he’s gone five innings. In those five innings, he’s bolstered his case, allowing just one hit, no runs, and no walks while striking out two.

Obviously, five spring training innings add little to the “can Heilman start?” discussion, particularly since he didn’t even really have to face a lineup twice, which is the big “if” with reliever-to-starter conversions. The five solid innings do, however, give Heilman a greater likelihood of seizing a rotation spot, for better or worse, so it’s probably a good idea to see if he’ll be able to hold on to his dream job if he can get it.

Heilman’s fastball has consistently sat at 92-94 mph in relief, but it was in the 88-91 range as a starter, which is quite fringy. It’s difficult to know how effective it would be in that role, as 2003-05 effectiveness data (which was mixed) isn’t exactly much of a help for 2011.

The only real data we have from Heilman pitching as both a starter and reliever in the same season comes from 2005, when he made seven starts and 46 relief appearances. That year, he had a 3.95 FIP as a starter and 2.35 as a reliever, although part of that was due to wonky HR/FB rates–his xFIPs were 3.67 and 3.15, which, for what little they’re worth, point to starting as a viable option.

But let’s move past that very limited data and look at this more practically. The first thing we need to figure out is whether Heilman can deal with opposite-side hitters. His strikeout rates against lefties and righties are essentially equal for his career, and from 2010, although he’s usually struggled with walks and homers to lefties more than he has to righties. Still, given that he has the changeup there to deal with lefties, and that his platoon split isn’t unreasonable, he’s unlikely to melt down for that reason.

More of a problem for Heilman, however, is that his fastball and changeup are his only two weapons. The changeup is nice, but he threw it 34.8% of the time last year, which works okay when you’re just in for 20 pitches, but perhaps less so when hitters see that applied to 100-pitch outings. Since his fastball likely would drop into the mediocre 88-91 mph range, it likely wouldn’t be terribly compelling in thwarting batters from sitting on the changeup.

No, if he’s going to find success in the rotation, Aaron Heilman is going to have to prove that his slider is a big-league pitch. Relief work has kept him, by and large, from needing to do that, as he basically never threw it in 2006-07 and has only thrown it in moderate doses the past three years, with a 10.1% usage rate this past season. It’s easy to see why he doesn’t use the pitch–it only got whiffs about one in every 21 throws, and it got him a far lower strike rate than his fastball or changeup. In short, it was easily his worst pitch–and that’s when hitters were never looking for it. Even with the element of surprise, there wasn’t much the slider could do.

So what does Heilman do as a starter? If he stays in his current 55-35-10 pitch distribution, hitters are going to sit on the changeup, and the fastball and slider aren’t going to be enough to get them off of it. If he switches to something like a 65-20-15 distribution, then the changeup may work better, but that leaves 80% of his pitches to be filled by fastballs and sliders, which isn’t likely to end well.

Furthermore, Heilman is an extreme flyball pitcher working in Arizona, which can be overcome in relief (when you can play the matchup game with him) but less so as a starter. With even less velocity and more predictability as a starter, those flies will likely be headed over the fence more.

When minor league pitchers come up, we often talk about them needing a changeup to combat opposite-side hitters or risk a bullpen future. Ironically, Heilman’s got that part solved, but his viability as a starting pitcher is jeopardized by his lack of more widely-possessed attributes like a decent breaking ball and groundball ability. Precedent for a pitcher like this succeeding as a starter does exist–see Rich Harden‘s 2008 (although Harden threw slightly harder, he had basically no third pitch)–but Heilman is seeking to be the exception, not the rule, and I wouldn’t bet on his coming through.

Of course, perhaps most importantly, over the past three seasons, Heilman has a cumulative WAR of -0.1 in relief, so why should we expect solid performance from him in a more difficult role?