If he doesn't he'll be spitting in the face of history.
We looked a couple times last year at Bryce's place in history. Did he have the best offensive season ever from a teenager? Did he have the most WAR from a teenage position player? These comparisons leave us with the obvious follow-up question : How did all these players we are comparing him to do in their sophmore seasons? We often hear about "sophomore slumps" but does that apply to the true phenom?
I'm going to look at guys that Bryce matches up with offensively (OPS+) and how they did offensively the next year. Why? Well, defensive stats bounce around too much from year to year. I'd hate to put up WAR, show all these guys improving but have it be because they lucked into awesome fielding years. Bryce is a very good fielder and is super fast. Those are constants. He'll have value. The question is more how much that value will increase (or decrease).
Player : OPS+ at age 19, OPS+ at age 20
Mel Ott: 139, 165
Tony Conigliaro : 137, 133
Ty Cobb : 132, 167
Sherry Magee : 122, 134
Bryce Harper : 119, ???
Mickey Mantle : 117, 162
Cesar Cedeno: 114, 97
Ken Griffey Jr : 108, 136
Edgar Renteria : 103, 80
Three players, Ott, Cobb, and Mantle, broke out to full superstardom. Two more, Magee and Griffey, improved a fair amount and would break out themselves, just not at age 20 (Griffey at 21, Magee at 22). I think this is the group we expect Bryce to be in. But what of the other three?
Cesar Cedeno is an odd case. His age 20 season would be his worst one until he was a hobbled 32-yr old trying to stay healthy enough to hang onto a job. He would then break out at 21 and would follow that with another superstar season at 22. He then would be involved in a situation where his girlfriend was shot dead in a motel room. He still played well after that but never to the same level. It may have been injuries, which is a concern because he played in an all-out fashion much like Bryce does. Then again, dead girlfriend. It's a cautionary tale in more than one way but probably not comparable to Bryce.
Edgar Renteria would show that that rookie year was kind of a fluke. (The BABIP was kind of high - though as a rookie you really don't know his level until he sets it). He'd have several mediocre seasons after that and while he'd occasionally have another good year for the most part he was a below average hitter. Edgar, though, was a completely different hitter than Bryce, dependent on high averages to make up for his lack of power. It's not a good comparison.
Tony Conigliaro is probably the most "worrisome" of comparisons. While he was still a good hitter he never really got past the level he had as a 19yr old. Now, there's a HUGE caveat here. He was having a slightly better year at 22 when he got beaned in the face. After that he was never the same player. Could he have been about to have his superstar year? Or was he just a "late" bloomer who would bust out at 24 or 25? We'll never know. Either way it's not like his 20-22 seasons were bad. They were in fact very good. Just not superstar level.
So what do the comparables say about Bryce? Simple, he will break out. Yes, yes small sample size but Bryce is such an elite talent he's going to be in small comparison groups his whole career. It could be this year, maybe 2014, but at worst by the end of 2105 he should have that great season. Five out of eight comparables had that big year by the time they were 21, with one more having it at age 22, and one possibly on the way to it at that age before a tragic injury derailed his career. Only Edgar Renteria, the last player on this list and not very comparable to Bryce, failed to make himself into a star. I have a hard time worrying about that.