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James Shields: Becoming an Ace

This might seem like a weird time to be writing an article about James Shields experiencing a breakout season, given that his 3.95 ERA this season is over a run higher than the 2.82 mark he posted last year. From a traditional standpoint, if Shields made an ace like leap, it was last season, and this year he’s simply regressing back to something less than ace-worthiness.

But, of course, I’m not exactly a big fan of ERA, especially when it comes to evaluating changes in pitcher performance. There are so many variables in ERA that a pitcher has little or no control over, and evaluating a pitcher by the amount of “earned runs” (whatever that means) he allows often causes us to miss real changes that do tell us something about what we should expect in the future. That looks to be the case with James Shields right now.

If you hadn’t looked at the batted ball leaderboards lately, you might not have noticed that Shields is currently fourth in the Majors in ground ball rate, coming in right between Jake Westbrook and A.J. Burnett. Shields has never been much of a GB pitcher, brining a career 43.8 percent ground ball rate into the 2012 season. This year, though, Shields has been one of the most extreme ground ball pitchers in all of baseball, and perhaps more amazingly, he’s done it while slightly increasing his overall strikeout rate from last season.

Strikeouts and ground balls generally don’t go together, as pitchers tend to specialize in getting one or the other. In fact, the average strikeout rate of the other nine qualified starting pitchers in the top 10 in GB% is just 13.8 percent, well below the league average and 10 percentage points below Shields’ mark. A.J. Burnett is the only starter in baseball this year with a top GB rate over 56 percent who is also posting an above average strikeout rate. The pitcher who can simultaneously get ground balls and strikeouts is a rare bird indeed.

A pitcher who combines very high ground ball and strikeout rates in the same season generally produce results that would put them in Cy Young contention in most years. In order to most accurately show the effectiveness of these types of pitchers, I went through and compared every qualified starting pitcher season since 2002 to that year’s league average ground ball and strikeout rates, and then determined how many standard deviations away from the mean that they were in those two categories. For instance, Derek Lowe is the most extreme ground ball pitcher we’ve seen in the last decade, while Randy Johnson is the modern day strikeout king, and both put up seasons that were three and a half standard deviations from the mean.

However, the king of combining these two factors was indisputably Brandon Webb. In 2003, his ground ball rate was 3.0 standard deviations above the norm, while his strikeout rate was 1.4 standard deviations from the mean. Randy Johnson in 2002 (3.5 StDevs in K%, 0.6 StDevs in GB%) was the only other pitcher in the last 11 years to put up GB and K numbers that were a combined four standard deviations from the norm. In fact, only 88 of the 995 (8.8%) qualified pitcher seasons since 2002 have resulted in a pitcher posting GB/K numbers that combined to be more than two standard deviations from the league norm in that year.

Right now, James Shields combination of GB rate (1.9 StDevs) and K rate (0.9 StDevs) is the 24th best mark since 2002 by when you look at ground ball and strikeout rates together. And pitchers who put up these kinds of GB/K rates at the same time are generally dominant forces on the mound.

There have been 26 pitchers who have posted a combined StDev of between +2.5 and +3.1, which gives us a decent sample of pitchers who as a group have the same 2.8 StDev total as Shields. In those 26 seasons, these pitchers combined for an ERA-/FIP-/xFIP- line of 74/73/72. To put that in perspective, Roy Halladay‘s career line is 72/75/74. Basically, the group of pitchers who combined for something like the amount of GBs and Ks that Shields is getting now put up results that would fit right into Halladay’s career.

Shields’ home run problem may prevent him from ever reaching Halladay-esque levels, but his HR/FB rate isn’t going to stay over 19 percent for much longer, and the fact that he’s added a significant increase in ground balls while keeping his BB/K rates stable suggests that Shields is simply getting better as a pitcher. It might not have shown up in the results so far, but Tampa Bay should be pretty thrilled about what they’re seeing from him so far this season.

He probably won’t keep getting ground balls at a Jake Westbrook type level, but he doesn’t need to sustain that kind of rate in order to become a legitimate ace. If he can keep his ground ball rate between 50-55% while also keeping his walk rate between 6-8% and his strikeout rate between 22-24%, he’d put himself in this group of pitchers who have put up those marks over the last 10 years: Felix Hernandez (2009, 2010, and 2011), Adam Wainwright (2010), and Josh Johnson (2009).

Shields’ ERA is deceiving – the way he’s pitching he’s right now suggests that he’s taken another step forward, and is on the verge of becoming one of the very best pitchers in all of baseball.