Originally written on Fangraphs  |  Last updated 11/19/14
Tonight, Mike Trout is going to be named the American League Rookie of the Year, and it’s almost certainly going to be unanimous unless one voter is just completely out of his mind. Bryce Harper is also likely to take home a rookie of the year trophy tonight, though his win isn’t as certain, nor will his margin of victory be as large. You can actually make a pretty good case for Wade Miley, and it wouldn’t be a travesty if he ended up pulling off the upset tonight. Harper was excellent, but he wasn’t the dominating force that Trout was in his first season in the big leagues. And yet, as we look forward to their respective careers, I’d still lean ever so slightly towards Bryce Harper having a better future than Mike Trout. If you look at Trout and Harper’s 2012 performances side by side, they’re actually pretty similar in most of the core statistics that hold up well from year to year. Name BB% K% ISO GB% Mike Trout 10.5% 21.8% 0.238 44.4% Bryce Harper 9.4% 20.1% 0.206 44.6% Here, the gaps are pretty small. Trout’s walk rate is a little better and his ISO is a little higher, but there aren’t major differences here. Their batted ball profiles are almost identical. In terms of the metrics that directly measure types of skills, there’s really not a lot separating Harper and Trout at the plate. The difference, of course, comes from all the small gaps in the other areas that Trout has adding up to a big overall advantage. Trout posted a .383 BABIP compared to Harper’s .310. Trout racked up +7 runs through effective base stealing and another +5 runs through non-steal baserunning, while Harper was basically a league average runner last year. Trout was a better defensive outfielder and spent more time in center field. As we’ve argued extensively during all the conversations about the AL MVP award, a player shouldn’t just be judged on what he does at the plate, but the total value he contributes to a team in every area. While Harper might have been similar in the batters box, Trout trounced him at everything that came after. But, those things all come with a caveat – they don’t hold up as well over the long term as the pure hitting skills do. We know that speed and defense peak earlier than power and patience, and we know that no matter how fast Trout is, he’s not going to be able to sustain a .380 BABIP over any significant period of time. Pretty much every advantage Trout has needs to be regressed more heavily in a future projection than the areas where they were already pretty close. For instance, let’s look at Trout’s baserunning value. Last year, his overall value on the bases was worth +12 runs, a truly remarkable total. That total has only been equaled 14 other times in the last 50 years, and no player has ever done it more than twice. Rickey Henderson — the greatest baserunner in the history of the sport — only topped +10 runs of baserunning value in a season four times in a 25 year career. For his entire career, he averaged +6.4 baserunning runs per 600 plate appearances. Even just limiting it to his peak years of 1980-1990, Henderson averaged +8.8 baserunning runs per 600 PA. 2012 Trout whomped in-his-prime Rickey Henderson by nearly 30%, which is both hilarious and a sign that he can’t possibly be expected to repeat that performance ever again. This doesn’t mean that Trout can’t remain an elite baserunner, or that we should expect his entire non-hitting advantage to disappear, but the margin of difference in 2012 overstates what can be realistically expected going forward. Even if we project Trout as a modern day Henderson with more power, we’re looking at a significant decrease in his value on the bases just from a glass ceiling effect, not even accounting for aging or injuries. The same is essentially true with his defense and BABIP, where there’s nowhere really to go but down. While it’s certainly fair expect Trout to improve his core offensive skills in order to offset some of the losses he’s going to sustain from regression, there are far more areas where he can get substantially worse than substantially better. The same is not true for Harper. His most projectable skill as a prospect has always been his power, which was often graded as a true 80 by scouts who saw him as an amateur. 80 power is extremely rare, and is reserved for guys like Giancarlo Stanton or Adam Dunn. This is a skill that often improves by leaps and bounds between a player’s teenage years and his peak, and while Harper’s .477 slugging percentage is impressive for a teenager in the big leagues, it’s nowhere close to fulfilling 80 power potential. In fact, just 39% of Harper’s extra base hits went for home runs last year, well below the 50% threshold that we often see from other guys tagged with 80 power. Stanton, for instance, has a career mark of 51%, which is why he’s slugged .553 with the same career batting average that Harper posted in 2012. It’s not at all unreasonable to expect Harper to add 50 to 100 points to his ISO as he develops, which would push him into +6 to +7 win territory even if he didn’t improve on any other aspect of his game. And, given what we know about players who can succeed in the big leagues at age 19, that’s not an assumption we should make. Of course, Trout isn’t exactly succeeding with old player skills either, and his dominance at age 20 is just as historically unique as Harper’s success at age 19. Both players look like once in a generation talents. To a large degree, this debate is hair splitting between greatness. It’s Ted Williams or Willie Mays, or Mickey Mantle versus Rickey Henderson. Barring some kind of injury, there’s a good chance you’ll be watching both Trout and Harper giving acceptance speeches in Cooperstown in 25 years. It’d be fun if they went in together, as they’re going to be inextricably linked for the rest of their careers. Given the choice over the guy who accumulated most of his advantage through speed and defense or the slightly younger guy with untapped power, though, I’ll lean towards the bat. I think both players have consistent +7 to +8 win seasons ahead in their primes, and both are likely to be among the best players in baseball for the foreseeable future, but I think there’s just a little more upside in Harper’s bat, and the advantages that Trout had in his rookie season are likely going down as career bests. I could very well be wrong, and maybe Trout’s unexpected power display in his rookie year suggests that we’ve all just underestimated his offensive capabilities. But, after one year in the books, I’d still prefer Harper by a very slight margin, even though Trout was demonstrably better in year one.
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