How Does Shelby Miller Compare to 2013 Starting Pitcher Averages?

The end of Cardinals starting pitcher Shelby Miller's debut season has come to overshadow what the rookie did before October. Miller put together a rookie year that earned him a third place finish in the National League Rookie of the Year voting, behind Dodgers phenom Yasiel Puig and electric Marlins starter Jose Fernandez. The Texan's Rookie of the Year finish was indicative of a well-below average ERA that belies less impressive peripherals.

The following charts compare Miller's 2013 stats to the NL starting pitcher averages for last season.

• A pitcher can get away with an average-ish walk rate (BB%) if he has a strikeout rate (K%) well above average. And that's exactly what Miller did in 2013. Miller's 23.4% K rate was high enough to rank 16th in the NL among qualified pitchers (and just ahead of teammate Lance Lynn, who posted a 23.1 K%).
• If we look at the Defense Independent Pitching (DIPs) stats of Fielding Independent Pitching (FIP), which is based on strikeouts, walks, and homers, and Expected Fielding Independent Pitching (xFIP), which is based on strikeouts, walks, and a league-average HR/FB rate, Miller had a less impressive rookie campaign than by Earned Run Average (ERA). This is interesting because ERA is more impacted by team defense than FIP or xFIP and the Cardinals were a substandard defensive squad last year, especially in the outfield. (You'll see below that Miller is very much a flyball pitcher.) Despite the Cards' bad defense, Miller managed to post an ERA that was substantially lower than either his FIP or xFIP. Miller's ERA-FIP gap of -0.61 was the 11th biggest in baseball and fifth largest in the NL. Kyle Lohse, who Miller replaced in the St. Louis rotation, managed a -0.73 ERA-FIP gap that was the fourth largest in MLB and second biggest negative ERA-FIP gap in the NL.
• By ERA, Miller's rookie year was perhaps more impressive than his peripherals suggest. Miller's strikeouts induced, walks issued, and homers allowed reflect a pitcher closer to league-average than his ERA suggests. Miller's ERA-, which is a stat that is league and park adjusted so that 100 is league-average and each point below 100 is a percentage point better than average, was 85. That's comfortably better than average. However, his FIP-, which is calculated on the same scale as ERA-, was 101 last year and his xFIP- was 99. These stats indicate that Miller's peripherals were about league-average even if his ERA was much better than average. (My charts compare MIller to NL starter averages because there is no DH. But the "minus stats" are based on the averages for MLB.)

• Miller did a good but not elite job of starting out a plate appearance by getting on top of the opposing batter. His 62.3% first-strike rate (1stStr%) tied him for 32nd in the majors and also tied for 21st in the NL.
• Miller is a severe flyball pitcher, which is okay in Busch Stadium III, as the Cards' home park tends to suppress offense. Miller's 41.3% flyball rate ranked fourth-highest in the NL and sixth-highest in all of baseball. Between his FB% and K%, a Duncanite Miller is not.

What does this mean for Miller going forward? Miller's 2013 appears unsustainable so long as his peripherals remain the same. That being said, if Miller were to follow staff ace Adam Wainwright's lead and cut his walk rate or further develop his secondary offerings and increase his strikeout rates (or both), an ERA on par with 2013 is not out of the question. The following charts show what the various publicly released projection systems forecast for the Redbirds' young righthander.

It's telling that all three of the projections available on Fangraphs forecast Miller's ERA to rise in 2014. It's just a question of how much. Without improved peripherals, fans should expect Miller to allow more runs his second year in the big leagues than he did as a rookie.