As Joe Sheehan pointed out elsewhere on SI.com, Sunday marked the one-year anniversary of the day that Mike Trout and Bryce Harper were called up by the Angels and Nationals, respectively, kicking off seasons that set new standards for what players of their tender ages could accomplish and culminating in Rookie of the Year honors for each. Forestalled by a spring illness and a roster logjam, Trout's callup marked his return to the majors after a 40-game stint the previous season. Harper's callup marked the beginning of his big league career. For the rest of us, it was the dawn of an era that hopefully lasts a long, long time.
Independent of each other, both Trout and Harper could be called once-in-a-generation talents. Trout, at 21 the older of the pair by about 14 months, had the better 2012 season, hitting .326/.399 /.564 with 30 homers and a league-high 49 steals in just 139 games. Even with the late start, his 10.9 Wins Above Replacement didn't just lead the majors, it was the best showing by any player since 37-year-old Barry Bonds — a man 27 years Trout's senior — tallied 11.8 WAR in 2002, and the best age-20 season showing of all time.
Harper, who hit .270/.340/.477 with 22 homers and 18 steals in 139 games, didn't garner serious MVP support the way his counterpart did, but at 19 years old, he nonetheless put up the greatest teenage season in history, with more total bases, extra-base hits, and WAR than any under-20 player ever had.
Of the two players, it's Harper off to the hotter start thus far. He homered twice on Opening Day, collected two hits seven times in his first nine games, and at this point is hitting a searing .360/.444/.756 — second in the NL in all three categories, for whatever that's worth — with nine homers in 99 plate appearances. This month has been by far the hottest of his young career, eclipsing last September's .330/.400/.643 showing.
The sample is obviously small, but aside from riding an unlikely-to-be-sustained 61-homer pace and not running very often (just three stolen base attempts so far, compared to 24 last year), what stands out in looking at Harper's batting line are his strikeout and walk rates. To date he's walking 12.1 percent of the time and striking out 15.2 percent of the time, while last year, he walked in 9.4 percent of his plate appearances and struck out in 20.1 percent of them. A 2011 study on statistical stability by Derek Carty of Baseball Prospectus show that such rates are among the earliest to stabilize, which is to say that even in smaller sample sizes than a full season of data, actual performance become more predictive of future performance than league averages or career averages. For strikeout rate, such a point comes when a player has 100 plate appearances minus unintentional walks minus hit-by-pitches, while for unintentional walk rate, the point comes when a player has 168 of the same. Harper's not at either of those cutoffs yet, but the early data suggests improvement in both plate discipline and contact rate, which would be a nice trick to pull off.
Harper's hot start hasn't put the Nationals — whom four of seven SI experts (myself included) picked to win the World Series — over the top. They're just 13-12 so far, averaging a meager 3.72 runs scored per game, and they've actually been outscored by 11 runs. By comparison, when Harper was recalled last year, the Nats were 14-6, and while their offense was similarly sluggish (3.55 runs per game), they had outscored opponents by 18 runs thanks to better run prevention. Aside from Harper, only Ian Desmond (.295/.313/.516) and Kurt Suzuki (.241/.354/.463) have been particularly productive with the stick; take away Harper's performance and the rest of the Nationals are hitting a combined .222/.282/.359 with 18 homers in 25 games.
Trout is off to a more middling start, hitting .263/.330/.424 with two homers in 112 PA. He's not running very often either, with just five attempts compared to 54 in 2012. In addition to not showing as much power as last year, his batting average on balls in play thus far has been 67 points lower than a year ago, when it was .383; Harper's, on the other hand, has risen 90 points to .360. That .383 mark is on the far edge of sustainability; in the 20 seasons since MLB expanded in 1993, 28 hitters have bettered that mark while qualifying for a batting title.
The Angels, meanwhile, are already in a 9-15 hole, which is at least better than the 6-14 mark they had compiled when Trout was recalled last April, but still a dangerous spot to be in if history is any guide. They're scoring just 4.04 runs per game, 11th in the league, in large part because Albert Pujols (.244/.343/.367) and Josh Hamilton (.219/.267/.323 ) haven't matched expectations. A bigger problem has been the pitching staff, which ranks 13th in the league at 4.96 runs per game allowed, and which is likely to be without top starter Jered Weaver for another month as he recovers from a nondisplaced fracture in his left elbow.
With their differing fates thus far this year — not to mention Trout's struggles during his 2011 stint — it's worthwhile to look at what the two did through their first 162 major league games, a point Trout reached last Sept.14, but that Harper just reached on Saturday:
That's a lot closer than last year's stats would suggest, with the gap of 146 points of OPS cut down to just 32. Trout had the big edge in stolen bases, but Harper owned the slightly better unintentional walk (9.7 percent to 8.6 percent) and strikeout rates (19.2 percent to 21.2 percent) as well as isolated power (.234 to .222) to that point. Keep in mind that the age difference in those two samples is substantial: 86.3 percent of Harper's plate appearances in that line above were compiled while he was still 19 years old, compared to just 6.7 percent of Trout's sample.
One month hasn't settled the argument of who's better, and of course, what Trout and Harper have accomplished goes well beyond the numbers. Both have put up a slew of highlight-worthy plays on defense (particularly the former) and displayed baseball IQs that belie their lack of experience. If one may be this generation's answer to Willie Mays, the other its Mickey Mantle (minus the drinking and womanizing, let's hope), and if we're lucky, we'll get to spend the next two decades charting the achievements of both.