He had a total of 241 PA prior to his age 19 season.
So while he wasn't a rookie, he was essentially just that.
During those 241 PA, I'm sure he adjusted to Major League pitching, so it hardly seems fair to compare them. I'm sure the rookie cutoff is there for a reason.
With 0.3 WAR earned yesterday, it looks more like Harper has a shot at Ott.
