Chase Anderson has quickly become a fan favorite, largely by winning his first five starts. Mike Bolsinger seems to be a bit of a punch line. But is Anderson really that much better than Bolsinger? Or, as I recently posted in a comment, "We just consider his performance to be worse than Anderson's because Anderson had a great debut, Bolsinger a poor one, and we judge way too quickly".
By traditional metrics, Anderson is far better. His 6-4 record is complemented with an ERA of 3.64, in ten starts with 54.1 innings pitched. Bolsinger is 1-5 with a 5.13 ERA in 47.1 innings pitched (over 8 starts and 1 relief appearance). But dig a little deeper and the story changes.
First, a look at FIP. We all remember the arguments about Brandon McCarthy's FIP, and how by that metric he should have been far more successful. Bolsinger ranks right behind McCarthy in FIP, second among D-backs starters at 3.89. Chase Anderson is in last among starters, and only 13 points better than current whipping boy Addison Reed at 4.70. FIP essentially reverses their places.
Look at HR/9, and it changes the picture still further. Bolsinger has allowed 1.1 per 9, which is league average, and trails only Collmenter and Arroyo among starters. McCarthy was at 1.2, Miley is at 1.3, and Anderson is at 1.5, once again the worst figure among starters, with only Addison Reed worse overall.
Looking at K/BB, Bolsinger is again league average (though substantially worse than either Miley or McCarthy) at 2.87. Anderson is at 2.47. Collmenter and Cahill struggle the most.
McCarthy, to no one's surprise, had the best GB/FB of the starters prior to being traded. What would surprise people is that Bolsinger is second, with his 1.17 behind McCarthy's 1.27. Anderson and Collmenter are tied for worst among starters, at 0.65.
To me, LD% really brings it home. While most of the D-backs pitchers are right around the league average of 25%, there are a few outliers. On the good end of the spectrum, Brad Ziegler is at 18%. On the other end, we find Anderson, at an astounding 36%! Addison Reed has only managed a 31%. Collmenter, for reference, is just above league average at 26%.
What does this mean? For starters, going forward, Bolsinger seems like the better bet, if these peripherals hold. The GB/FB and LD% are especially disconcerting. Typically, you can succeed as a fly ball pitcher if players aren't making good contact, as can be seen with Collmenter, who is an extreme flyball pitcher but has a low HR/9 (0.9). Anderson has been successful thus far despite his high HR/9, which is the product of being a fly ball pitcher with a high LD%. But that is simply unsustainable. Unless he finds a way to fool more batters (which could happen, as he seems to have the pitches to do it), he simply cannot continue to get the job done. The list of pitchers with a LD% of over 30% and an ERA under 4 can't be very long. Bolsinger, on the other hand, has been so comparable to McCarthy that it really looks like there might be more than luck involved. Could the defense, which looks good, really have a problem (most likely in positioning)? I could see one pitcher with McCarthy's peripherals and results, but two in the same season screams that there must be an underlying cause. And while McCarthy's problems could be blamed on the long ball and the big inning, Bolsinger's cannot. True, Bolsinger has a couple of big innings, but it hasn't been the epidemic with his starts like it was with McCarthy's.
Hopefully, either Bolsinger or Anderson will be the 5th starter next year. Hopefully they will both have nice careers. But at the moment, in the discussion of who is better out of two players that should never be aces, the answer has to be Bolsinger.