Yea, Mike Bolsinger's primary "hard" pitch is a cutter that goes 87.5 mph on average, but who cares? Chris Young's fastball crawls through the air while other fastballs sprint, but he seems to do OK. An evaluation of a pitcher can start with his stuff, but it certainly doesn't end there.
Starting with his stuff, the right-handed Bolsinger throws his cutter about half the time. His other two pitches, a curveball and a slider, take up the rest of his repertoire. For those of you counting at home, those are three pitches that aren't a changeup. As you might expect, Bolsinger had himself a little platoon split last year:
vs. L - .348 wOBA
vs. R - .278 wOBA
Luckily, teams can't throw out nine left-handed hitters, so Bolsinger will get his fair share of right-handed destruction. The platoon split will most likely be an issue, despite the small sample size of his MLB career so far, so that's definitely a ding on his resume.
However, look at the overall results. In 109.1 innings, Bolsinger managed a 3.62 ERA, a 3.91 FIP, a 3.82 xFIP, and produced a 1.2 fWAR; which works out to about 2.2 fWAR/200 innings. Despite the low velocity, Bolsinger still managed to strike out more than MLB average for starters (21 percent vs. 19.5 percent). He lost a bit of that value through a higher than MLB average walk rate, but he also had a 53.1 percent ground-ball rate; which was the 15th best rate out of 133 starters with at least 100 innings in 2015.
The projections buy his past success, and are confident in Bolsinger going forward. Steamer forecasts a 3.79 ERA and a 3.74 FIP; and ZiPS is essentially in perfect agreement. PECOTA sees a 3.74 ERA. Marcel is the highest of the four main systems with a 4.01 ERA. Where the systems all differ is in playing time.
Steamer - 45 innings. PECOTA - 95 innings. Marcel - 119 innings. ZiPS - 143 innings. That's almost a 100 inning difference between the lowest and highest projections. Clearly, Bolsinger's talent isn't in question. It's his place in the rotation.
Well...that rotation became a little less clear with the injury to Brett Anderson. Clayton Kershaw sits at the top of the rotation, and he's followed by Scott Kazmir and Kenta Maeda. Alex Wood, also an above-average starter, slots into the fourth spot. The fifth spot is then between Bolsinger, Brandon Beachy, and Carlos Frias. Zach Lee and Ross Stripling are also in the mix.
Beachy has some injury issues of his own - two elbow surgeries later, it's unknown if he'll be able to contribute in a significant way in 2016. Frias might fit better in the bullpen, as he struggled to get strikeouts in the majors last season. Lee is a 24 year old who has logged significant time at AAA and may be ready to graduate to the big-league club after a good performance in 113.1 innings in AAA last year, but he's made only one start in MLB. Bolsinger has more experience. Stripling has not yet pitched above AA. 23-year-old prospect Jose De Leon may get a look as well, but he has not logged a single inning above AA either. Julio Urias also gets mentioned, but the kid is only 19. He needs to log more innings to build up strength; he may find himself on the big-league club later in the year if he really wows people in the minors. Despite multiple options, the most prudent course of action is undoubtedly to slot Bolsinger into the rotation.
What complicates Bolsinger's role in the future is Hyun-Jin Ryu, who was very good in 2013 and 2014 but has had shoulder issues keeping him off the field since then. Ryu, should he return healthy, would take a rotation spot and slide everyone else down; forcing Bolsinger out of the rotation. Ryu recently "experienced discomfort in his surgically repaired left shoulder" but he began throwing again. His timetable for a return is potentially in May, but shoulders are finicky and extremely worrisome injuries for all players, especially for pitchers. If he's experiencing discomfort, his performance upon his return is questionable.
That leaves Bolsinger as the best option now and for perhaps two months or more. It sure is nice to be a Dodgers fan; the fifth starter, whose job may be in jeopardy upon the return of a better player, is roughly an MLB-average pitcher. MLB average in the fifth spot is pretty good.