What Should We Expect From St. Louis Cardinals Reliever Mitchell Boggs This Season?

The 2012 St. Louis Cardinals bullpen gave fans more to jeer than cheer for a large chunk of last season. Disappointment abounded, from Marc Rzepczynski pitching worse as a National League Central reliever than he did as an American League East starter to Fernando Salas's bad batted-ball results to Victor Marte. One of the relief corps's few bright spots from Opening Day through October was righthander Mitchell Boggs.

In 2011, Boggs was a bullpen backbencher, used by then-manager Tony La Russa primarily in low leverage situations. The righty's statistical profile fit the role rather well. Boggs induced swinging strikes (SwStr%) at a below average rate and, perhaps consequently, also struck out opposing batters at a lower-than-average rate. To his credit, Boggs walked batters at a lower than average clip while inducing grounders with a high frequency.

BOGGS 2011 STATS

In 2011, Boggs allowed runs at a higher rate than his strikeout and walks allowed totals would suggest. This is reflected in his FIP, which is calculated based on K, BB, HR, and IP, without considering any other types of balls in play. The fact that Boggs allowed homers on fewer flyballs than your average reliever allowed his FIP to outperform his ERA. However, when his HR rate is adjusted to be the league average in the xFIP formula, we see that his ERA was a bit lower than to be expected.

In 2012, Boggs upped his K% by one point and lowered his BB% by a point. Batters saw their fly balls against Boggs carry out of the park at a rate one percentage point higher than in 2011. Nonetheless, Boggs's 2012 peripherals are remarkably consistent with what he posted in the year prior. Boggs' fielding-independent metrics are nearly identical.

BOGGS 2012 STATS

Despite many similarities between Boggs's 2011 and 2012 stats, there is one big difference: ERA. Despite posting a FIP just two points lower than it was in 2011 and an xFIP a mere two points higher, Boggs's 2012 ERA fell by a whopping 135 points to 2.21. This ERA drop created a yawning ERA-FIP gap of 1.21. As we touched on last week when looking at Adam Wainwright's 2012 struggles, FIP and xFIP do not consider hits other than homers because of the influence a pitcher's defense has on such plays. It isn't surprising then to find out that the balls put in play by opposing batters against Boggs fed his decreased ERA.

OPPOSING BATTERS VS. BOGGS (2011 & 2012)

In 2012, opposing hitters saw their average against Boggs drop by 55 points, on-base percentage fall by 50 points, while they slugged for 91 fewer points and their Weighted On-Base Average (wOBA) crater. The primary culprit for the difference in the 2011 and 2012 hitting lines against Boggs is our old friend Batting Average on Balls In Play (BABIP).

The question now becomes whether Boggs saw his batted-ball profile change in a way that would support a 69-point drop in BABIP. It doesn't. There are some fluctuations that likely should have a slight overall decreasing effect on BABIP, but it would be minor. There's no reason to think opponents' .245 BABIP against Boggs in 2012 is anything other than the type of mirage so often found in reliever stats.

BATTED-BALL PROFILE FOR BOGGS (2011 & 2012)

In addition to the fielding-indpendent measures of FIP and xFIP, folks have come up with stats that attempt to create a pitcher's expected ERA based on his batted-ball profile. One of these stats is called True Runs Allowed; or, tERA. The Fangraphs Glossary entry for the metric explains it thusly:

True Runs Allowed (tERA) is a defense-independent ERA estimator built by Graham MacAree from StatCorner that was designed as an alternative to FIP and xFIP. The most common complaint about FIP and xFIP is that they completely ignore performance on balls in play, while batted balls can still tell us something about a pitcher's skill level: groundballs are good (since they normally result in outs), flyballs have a higher probability of resulting in extra basehits, pop-ups are almost guaranteed to be outs, and line drivers are the most likely type of ball in play to end up as a hit.

tERA includes all of these variables, and is based on the same scale as ERA, FIP, and xFIP. It is a little less accurate in predicting future performance than xFIP, but it is still more valuable than ERA and provides us with another lens through which to evaluate pitchers.

The Fangraphs Glossary entry for SIERA explains the complicated formula used to calculate the metric:

Skill-Interactive ERA (SIERA) is the newest in a long line of ERA estimators. Like it's predecessors FIP and xFIP, SIERA attempts to answer the question: what is the underlying skill level of this pitcher? How well did they actually pitch over the past year? Should their ERA have been higher, lower, or was it about right?

But while FIP and xFIP largely ignore balls in play -- they focus on strikeouts, walks, and home runs instead -- SIERA adds in complexity in an attempt to more accurately model what makes a pitcher successful. SIERA doesn't ignore balls in play, but attempts to explain why certain pitchers are more successful at limiting hits and preventing runs. This is the strength of SIERA; while it is only slightly more predictive than xFIP, SIERA tell us more about the how and why of pitching.

The following chart contains Bogg's ERA, FIP, xFIP, SIERA, and tERA, which can all be found at Fangraphs.

DEFENSE-INDEPENDENT METRICS FOR BOGGS (2010-2012)

The only outlier is ERA, which is the only stat affected by fielding. The fielding-independent stats both see Boggs as a pitcher who should fall in the mid-3.00's on the ERA scale. The more advanced defense-indpendent stats, which consider a pitcher's batted-ball profile, see him in much the same way. Given the mid-3.00's range given Boggs by FIP, xFIP, SIERA, and tERA, I was a bit surprised by some of the projection system forecasts for him in 2013.

2013 BOGGS PROJECTIONS

I was a bit surprised to see the Bill James and PECOTA forecasts for Boggs so negative. On the other hand, the ZiPS, Oliver, and Steamer projections feel about right. Other than the hope that the gods of baseball again see fit to grant Boggs a consecutive season of good reliever volatility, there is no reason to expect Boggs to put up a sub-.300 ERA this season. The defense-independent pitching metrics and forecast average suggest he is a pitcher likely to post an ERA in the mid-3.00's. Fans should adjust their expectations accordingly.