In the past two years, Shelby Miller descriptors have run the gamut: a can't miss prospect, a struggling minor leaguer, a too lean gym fiend, rotation mainstay, candidate for top rookie, near perfect pitcher, off limits, trade bait, playoff 'pen-session expert, and post-season ghost. Miller's rookie year was memorable, for better and worse, but as he moves into his second year expectations are raised. Based on similar players, raised expectations might be unfair.
As a 22-year old rookie, Miller pitched 173 ⅓ innings with 8.8 K/9, 3.0 BB/9, 1.0 HR/9, 3.06 ERA, 3.4 rWAR and 2.1 fWAR. Looking at the performance of prior players after comparable rookie seasons should provide some insight regarding Miller's sophomore season. I ran two searches, one on baseball-reference and one on fangraphs. For each search I looked at 22 and 23-year old rookies from the previous 30 seasons who pitched between 160 and 200 innings. For baseball-reference, I looked for players with an rWAR between 2.4 and 4.4. For fangraphs, I looked for players with an fWAR between 1.6 and 2.6.
Here is the fWAR group:
Here is the rWAR group:
At first glance, Miller's rate numbers look better than these groups as a whole. Varying run environments do play a role which ends up resulting in the WAR similar to Miller. While the fWAR of the group overall is pretty consistent, fWAR was not kind to the rWAR group, depressing those numbers when looking at the overall averages. Due in part to Miller's gap between fWAR and rWAR, there are only two crossovers, Joe Mays and Pete Smith. As you can see below, the group as a whole did not fare well in season two.
The rWAR group fared better than the fWAR group, but the rWAR group started with a higher baseline. The average numbers are weighed down by some terrible return seasons due to injury, ineffectiveness and both. While injuries are always possible, it could be valuable to isolate the above group and look only at those players who pitched close to a complete season. Here are the numbers for the players who pitched at least 150 innings.
This group is considerably more encouraging. Of the thirteen players who pitched close to a full season, eight turned in at least average performances with only Scott Olsen and Melido Perez having a disaster of a season. If Shelby Miller can remain healthy, reproducing 2013's solid numbers appears attainable. Expecting him to transform into an ace this season is on the optimistic side. The sophomore seasons from Pettitte and Verlander show great possibilities, but that is clearly the best case scenario.