To look at how great young hitters did in the years immediately after their high OPS+ season, I had the Baseball Reference Play Index call up all the players age 23 or younger who had at least a 170 OPS+ with a minimum of 400 PAs.
The table below shows what they did at either age 22 or 23 and then the next three seasons. Avg is actually their OPS+ over the next three years combined, not a simple average.
|Ken Griffey Jr.||171||23||171||122||154||153|
There are 26 cases but some player appear more than once (Mathews, Trout, Musial, Williams, Cobb). So if we only look at the number of players instead, we have 20 cases. 13 of those 20 players had at least one season of a 170 OPS+ or higher in the next three years (starting from the first season they did it-Mathews did it first at age 21 and did it again at age 22 & 23 but not at 24, 25 or 26).
So most young players who have a great season have another one pretty soon after. Not Harper. His best season of the next three is 156.
The next table shows the difference between each player's great young season and the average of the next three, sorted by largest gain down to biggest decline.
|Player||OPS+||Age||Avg of next 3 seasons||Diff|
|Ken Griffey Jr.||171||23||153||-18|
So Harper has the biggest drop off and he seems well ahead of the next biggest decliner, Powell. Considering how well he did at age 22 and where that ranks historically for young hitters, his performance the last three years may look disappointing.
I also looked at all players who had 1200+ PAs from ages 20-22 and an OPS+ of at least 140. Then I found their OPS+ over the ages 23-25 (not exactly, for example, Ted Williams missed three years in WWII so for him I just used his next three seasons).
Harper had an OPS+ of 154 over ages 20-22 and 133 over ages 23-25. That drop off of 21 is the 2nd biggest among this group of 22 players. In fact, 16 of the 22 actually did better over the next three seasons and the last time anyone dropped off as much as Harper was in the 19th century (Beckley). Pujols, Griffey and Trout are all fairly recent players who increased their OPS+ going from 20-22 to 23-25. Yet Harper has this big decline.
|Player||OPS+ 20-22||OPS+ 23-25||Diff|
|Ken Griffey Jr.||146||161||15|
Where does Harper's 133 OPS+ rank all-time among 23-25 year olds who played at least half their games in the outfield with 1200+ PAs? 81st out of 99.
Click here to see that list