Analyzing Mark Trumbo's Powerful Start

Mark Trumbo started the season with six home runs in 16 games.

Note: All numbers compiled before last night's slate of games.

Although he has a two-game head start, Mark Trumbo is currently the Major League leader in home runs. If you combine runs scored and runs batted in, Trumbo’s 28 narrowly edges those Giancarlo Stanton and Adrian Gonzalez, who each have 25. There is no denying that despite his anemic .275 OBP and -0.2 WAR, Trumbo appears to be headed toward a terrific season, speaking in purely fantasy context.

However, just by logging onto numberFire, you have heard that past performance is not always the best indicator of future performance. The Law of Large Numbers states that, in the short term, results are random, but over a long period of time, the total results move closer and closer to the mean. In essence, regression will always take place, even if we do not who exactly when it will occur.

If you would like to read more about regression, check out this article by our Editor-in-Chief JJ Zachariason. In this piece, we'll analyze and interpret Trumbo’s plate discipline, batted ball data, and home run data to determine whether his performance is legitimate.

Plate Discipline

With three seasons already under his belt prior to his offseason trade to the Diamondbacks, Trumbo established himself as a swing-hard, miss-hard type of guy. He averaged 152.3 punch-outs annually from 2011-2013, or 24.9% of his plate appearances.

More often than not, I hear Trumbo compared to Adam Dunn, which I fail to understand because Dunn is a Three True Outcomes player and Trumbo has only walked on 6.2% of plate appearances in his career. Really, the three biggest similarities between the two players is that they strike out often, are terrible defenders, and can hit for power. However, Dunn is a rare type of player and is much more durable than Trumbo.

This season, Trumbo has struck out on 24.6% of his plate appearances, which is roughly in line with his three-year average. While his 2014 walk rate of 5.8% looks like a decrease from his three-year average of 6.8%, we have to remember that we are dealing with small sample sizes; add one more walk to his total and it increases his rate to 7.2%. Essentially, Trumbo is striking out and walking about as often as he has in the past. Looking at PITCHf/x data, his chase rate and contact rate on pitches inside the strike zone are also on par with career numbers.

Based on the data observed, I have no reason to believe that if there is a change in Trumbo’s skill level, that it has been caused by a change in plate discipline.

Batted Ball Data

In order to hit home runs, batters must hit fly balls. To me, Trumbo doesn’t seem like the type of player who can hit inside-the-park-homers on ground balls. Two of the leaders in fly ball percentage are Brandon Moss and Chris Davis, who hit 51.8% and 45.7% of their 2013 batted balls into the outfield air, respectively. That approach worked pretty well for them, as they combined for 83 home runs last year.

While Trumbo is on pace for 61 home runs this season, he's hit 51.1% of his batted balls on the ground, compared to only 31.9% in the air. These numbers deviate from his career percentages of 45.6% and 38%, respectively. It seems almost counterintuitive that Trumbo is hitting more home runs despite hitting fewer fly balls.

HR/FB is the ratio of home runs to fly balls hit, which is an indicator of power that is ideal for examining small amounts of raw data. This ratio varies from year-to-year and allows us to locate luck in home run totals to a certain degree. You can read more about HR/FB here.

For example, Player A might go 1 for 4 with three groundouts and a home run in each of his first two games. This would give the player a HR/FB of 100%. If Player B goes 1-4 with three fly outs and a home run, he would have a HR/FB of 25%. Although 25% is still very high and we need more context before reaching a final conclusion, Player B is more likely to sustain his rate, mostly because it is unreasonable to expect Player A to homer on every fly ball.

According to FanGraphs, the league average HR/FB is about 9.5%. From 2011-2013, Trumbo’s HF/FB was 19.8%, good for 13th in MLB over the interval. This season, Trumbo has converted 6 of 15 fly balls into home runs, meaning he has a 40% HF/FB. In 2003, Barry Bonds hit 73 home runs with a HR/FB of 29.6%. It's a safe assumption that Trumbo’s end-of-season HR/FB will be closer to 19.8% than 40%.

It seems reasonable that Trumbo’s 2014 home run total may have been fluky thus far. As a side note, the .219 batting average should move north for summer once the .195 BABIP regresses.

Home Run Data

One positive aspect of Trumbo’s move to Arizona is that he moved to Chase Field, a hitter’s park, from Angel Stadium, a pitcher’s park. It makes sense that a home-run hitter could hit more home runs if his environment improved. However, I used ESPN’s home run tracker to analyze the distances of Trumbo’s home runs, and noticed that four of the blasts carry question marks.

The first one was Trumbo’s first 2014 homer, off Kenley Jansen on March 22 in Australia. It only traveled 347 feet to straightaway left and would not have been a home run in any MLB park.

Of the five other round-trippers he's hit this season, three of them were at the hitter’s paradise known as Coors Field. Trumbo homered in all three games in the series, which definitely makes me curious as to what he could do in 81 games there. Unfortunately, Trumbo only has 10 more games this season against the Rockies at Coors. While it seems unfair to penalize Trumbo for his good performances at Coors, it's also unreasonable to make predictions off five series, one of which was played in the park most suited to right-handed power hitters.

Should you assume Trumbo’s four question-marked homers went as fly outs instead, his HR/FB would be 13.3%. If we estimated 600 at-bats over the season minus the 64 he has already, then subtracted predicted strikeouts, we would estimate Trumbo putting 408 balls in play. For this exercise, we will assume Trumbo’s fly ball rate stays at this year’s 31.9% instead of his career 38%. He would have 130 fly balls. Assuming his conservative 13.3% HF/FB sticks, we would predict 17.35 home runs over the remainder of the season. For a conservative estimate, Trumbo still looks to be an above-average contributor in the category.


Based on the data, Trumbo’s home run numbers appear to be the result of a fluke, and he'll have trouble sustaining close to this pace throughout an entire season. And that's not even accounting for Trumbo’s reputation as a guy who tends to break down during the second half of seasons, something he's done in each of the past three years. This could be your best chance to sell high on a guy whose surface stats are due to decline soon.