How worried should the Cardinals be about Shelby Miller’s sophomore slump?

Cardinals right-hander Shelby Miller is coming off one of his best starts of the year, Friday night’s seven-inning, two-run no-decision against the Cubs at Busch Stadium. That sentence alone speaks to how discouraging Miller’s 2014 has been. After a stellar rookie season earned him third place in NL Rookie of the Year balloting, the 23-year-old has endured a particularly rough sophomore slump, recording an ERA more than a full run higher than last year and routinely struggling to pitch out of the fifth inning.

Miller was briefly moved to the bullpen following the All-Star break, and the extra rest seems to have done him some good, but an 0-1 record and 4.01 ERA in seven starts since rejoining the rotation still leave a lot to be desired. In truth, he hasn’t looked consistently sharp in more than a year now, and a rocky end to the 2013 season led to his conspicuous (and for some, confounding) absence from much of the Cards’ playoff run.

It’s not just bad luck, either. Miller’s FIP (Fielding Independent Pitching) has ballooned from 3.67 last season to 4.89 in 2014, meaning he’s been even less effective this year than his top-line numbers suggest.

How worried should the Cardinals and their fans be by this turn of events? How common is it for pitchers to have such a strong first season but struggle so badly in their second? How often — as will hopefully be the case with Miller — do they overcome their sophomore struggles and regain the form they showed as rookies?

Since 1980, there have been 48 major-league pitchers who started at least 23 games and posted a sub-4.00 FIP in their rookie season, then started at least 23 games again the following year. On average, these pitchers recorded an FIP about 36 points higher in their second full season in the majors; roughly one-third of them experienced a significant sophomore slump, with an FIP increase of 70 points or more.

Aug 11, 2014; Miami, FL, USA; St. Louis Cardinals starting pitcher Shelby Miller (40) looks on during the fifth inning against the Miami Marlins at Marlins Ballpark. Marlins won 6-5. Mandatory Credit: Steve Mitchell-USA TODAY Sports

Seven of these outstanding rookies slumped so badly in their second season that their FIP jumped by at least 100 points — and unless he improves dramatically over the course of his last four starts, Shelby Miller is about to become the eighth.

In other words, agonizing over Miller’s poor performance this year is perfectly reasonable. His 2014 campaign, as of last Friday’s outing, is the fourth-worst follow-up to a solid rookie season in the last 35 years. That’s not a drop-off that can be easily waved away.

Still, if history is any indication, there’s plenty of time for Miller to turn things around and become the ace many expected him to be. By far the worst sophomore slump among pitchers in the last few decades was suffered by Seattle southpaw Mark Langston, who had a dreadful second season in 1985, posting a 6.01 FIP and a 0.79 K:BB ratio, but went on to have an exemplary big-league career, earning four All-Star nominations and providing more than 50 WAR in fifteen seasons as a starter for the Mariners and Angels.

Of course, other second-year declines weren’t merely speed bumps on the road to greatness; plenty of talented young pitchers hit a wall in their sophomore campaigns and never recovered. Another Mariners lefty,
Dave Fleming, had a great rookie season in 1992, slumped in 1993, slumped even harder in 1994, and was out of the majors by 1996. The Cardinals’ own Donovan Osborne saw his HR and walk rates climb in his second season and never quite recaptured the promise of his rookie year, pitching only one more full season as a starter before chronic shoulder problems gradually forced him out of the game.

Perhaps the most interesting name on the list of Miller’s fellow sophomore slumpers is former Diamondbacks ace Brandon Webb. There are some key differences between Webb’s and Miller’s pitching profiles; the former was a textbook sinkerballer, with an eye-popping career ground-ball rate of 64%, while the latter punched his ticket to the majors with his four-seamer.

What they do have in common is a heavy reliance on their preferred fastball, each throwing their respective pitch type well over 70% of the time. And while Webb’s second-year slump wasn’t as alarming as Miller’s — and came, it should be noted, on an atrocious 2004 D-backs squad that went 51-111 — he, too, was done in by an inability to control the strike zone and an inflated walk rate, giving free passes to a league-high 119 batters on the season.

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Comparing Miller to Webb, for whatever it’s worth, is reassuring in the short term and worrying in the long run. Webb put his sophomore struggles behind him and became one of the best pitchers in the game over the next four years, nabbing a Cy Young and three All-Star nods and posting a career ERA+ of 142, good for a tie for 12th on MLB’s all-time list. But he threw his last big-league pitch at the age of 29, in Arizona’s 2009 opener, his career derailed by a series of shoulder injuries. After four years spent trying to make a comeback, he officially retired last year.

And it’s injury that may be the next shoe to drop in the curious case of Shelby Miller. Whether or not it does may ultimately determine what the rest of his career looks like. Back tightness forced him out of a start in June; more seriously, shoulder issues were reported both shortly before and after last season, and the whispers that started during his October vanishing act haven’t abated. For now, of course, Miller will try to build off his recent success, and there’s little for Cards fans to do but ask questions only time can answer.