St. Louis Cardinals trade analysis: What do Brandon Moss's peripherals tell us about his ability to bounce back?

The St. Louis Cardinals acquired first baseman/outfielder Brandon Moss from the Cleveland Indians on Thursdays in exchange for lefthanded pitching prospect Rob Kaminsky. The Cardinals gave up a top-five prospect in their farm system for the rights to Moss through the end of the 2016 season. It was a higher prospect price than Cleveland paid during the winter because of the cost of marginal wins in July. In doing so, the Cardinals paid a premium for a bounce-back candidate.

After the Red Sox traded Moss to the A's, Moss emerged as one of the top power bats in baseball. However, the lefthanded slugger's batting production fell of significantly after moving to Cleveland.

Moss:  2012-15 Stats

Now on the wrong side of 30, Moss has seen his Batting Average on Balls In Play (BABIP) drop, which has caused a corresponding dip in his batting average (BA). His on-base percentage (OBP) and slugging percentage (SLG) have fallen as well. Isolated Power (ISO) is a stat that excludes singles and considers only extra-base hits. It has also fallen. Moss's batting production has steadily fallen across the board to a four-year low this season.

One theory explaining Moss's offensive decline has to do with his hip. Moss required offseason surgery on his hip to repair a torn labrum. St. Louis Post-Dispatch beat writer Derrick Goold interviewed St. Louis management and Moss regarding the trade. In the article that resulted, Goold reported that "Moss said he worked through some adjusted mechanics but felt good with his swing." So Moss's hip problems have led to a change in his swing (or process) that could be impacting his hitting results.

General manager John Mozeliak explained to Goold that the Cardinals performed extensive analysis of Moss's numbers before pulling the trigger on the deal:

Mozeliak described how there are questions about a deal when the Cardinals’ interest in a player is "not baseball-card stat-driven" but based on advanced placement metrics, like velocity off the bat or factors specific to a ballpark. The Cardinals are encouraged overall by Moss’ steady line-drive rate this season and how it compares favorably to the three seasons (2012-14) he had in Oakland with 21 or more homers. His strikeout rate hiked up this season, but other indicators of his swing remained similar. Home was where the hits weren’t.

We don't have access to the same information the Cardinals do. Their data on players' batted-ball profiles is more extensive than what is publicly available. They have exit speed and trajectory that likely allows for far more accurate and nuanced batted-ball classifications and assessments. Nonetheless, I thought it might be interesting to take a look at the public batted-ball data to see if it meshes with what Mozeliak shared with Goold regarding Moss.

Batted Ball Data

First, we'll start with line-drive rate (LD%). The MLB average LD% is usually in the 18-21% range. From 2012-15, it ranged from 20.8% to 21.2%. Moss's LD% dipped in 2013, but has been right around the MLB average rate. This year it is one-half of one percentage point less than the MLB collective LD% of 21.0% entering play on Sunday.

We don't have exit-velocity data going back far enough to make a useful comparison. Moreover, the exit-velocity data that MLB has released to the public is incomplete. What we do have is the three-buck system available for free at Fangraphs: Hard%, Med%, and Soft%. The MLB average Hard% is 26.9% and 32% over the last ten years. Here are the Hard% for the last four years: 2012, 28.5%; 2013, 30.5%; 2014, 29.1%; 2015, 28.5%. After a drop last year, Moss's Hard% is back around where it was in 2012 and 2013. It is also head and shoulders above average.

So how do we account for the steady drop in Moss's HR/FB rate? It's difficult to do.

Oakland tends to suppress homers mightily for lefthanded hitters—much more so than Cleveland. Moving to the Indians should have helped Moss's power numbers, according to the Fangraphs park effects, not hurt them. Yet Moss struggled mightily while playing at home at Jacobs Field. (That's what I call it.) Further, Moss's numbers fell from his breakout season in Oakland to year two to year three. That's difficult to pin on his hip alone.

Plate Discipline

This chart contains the following Pitchf/x stats: outside-the-zone swinging rate (O-Swing%); inside-the-zone swinging rate (Z-Swing%); outside-the-zone contact rate (O-Contact%); inside-the-zone contact rate (Z-Contact%); overall contact rate (Contact%); overall swing rate (Swing%); swinging-strike rate (SwStr%); strikeout rate (K%).

The stats here don't reveal much in the way of a compelling change in approach. It appears that Moss began being more selective when limited by hip troubles. This caused his Swing% to drop in 2014. It's back up. He is swinging as often as he did in 2012, including outside the zone. What's interesting, though, is that he is not swinging and missing as often, at least as measured by SwStr%. So while his K% has gone up, it's to a rate that falls in between his 2012 and 2013 strikeout rates.

Balls in the Air

All in all, it's not Moss's strikeouts that concern me. It's the lessening amount of damage he is doing when hitting the ball in the air—especially on fly balls.

The Cardinals have far more precise data on Moss's fly balls than what is publicly available. They know the mph on them and can compare that information year to year. That they have done so and nonetheless felt good about acquiring Moss makes me feel less concerned about the decreased potency on Moss's fly balls over the last four seasons.

That's not to say that i'm not worried. It could be his hip, perhaps age, or maybe luck. It's likely some combination thereof. Whatever the reason, I'm worried that the power-hitter the Cards acquired to make their lineup more potent has become less and less potent on the type of batted balls that are his bread and butter: flies.

A fly ball can land beyond the outfield wall for a hit (a homer, specifically) and it is not considered a ball in play for BABIP purposes. Thus, it's possible to have a high average on flies, though it isn't easy. The more homers a player hits, the higher his BA on fly balls is going to be. The same goes for his ISO and wOBA. All have fallen steadily on the fly balls Moss has been hitting. In 2015, Moss's fly-ball BA of .198 is below the MLB overall BA of .225. The same is true of his .414 ISO, which has dipped beneath the MLB overall fly-ball ISO of .419. To be the power-hitter that the Cards need, Moss is going to have to give his fly balls more of a charge.

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