Domonic Brown and the “illusion” of breakout seasons

I don’t read everything on FanGraphs, mostly because they publish a new article every 37 minutes and I have a full-time job. Sometimes more than full-time! But I am particularly interested in fundamental questions, so this item did pique my curiosity:

My immediate reaction, before clicking? “What’s a breakout, and what’s an illusion?”

The definition of “illusion” remains ethereal, but after clicking I discovered Jeff Sullivan’s definition of “breakout” ... a breakout is when a player’s OPS+ was 110 or lower in his Age 24 season, then jumped by at least 20 percent in his Age 25 season. As Jeff notes, those numbers are arbitrary. They also seem as good as any others. In one sense, they’re chosen to include Domonic Brown, who inspired the study.

Jeff looked at the last 50 years, and came up with 70 hitters. That’s a good-sized pool!

The results:

Pre-25: 94 OPS+
At 25: 130 OPS+
At 26: 114 OPS+

Maybe you only care about the biggest improvements. A dozen players improved by at least 50% in their age-25 seasons. This is how those players did:

Pre-25: 84 OPS+
At 25: 139 OPS+
At 26: 117 OPS+

No matter how you slice the numbers, the numbers go down in the age-26 seasons. At age 26, the players are better than they were before turning 25, but they’re worse than they were at 25, the next season falling roughly in between. It wouldn’t be fair to say that, as a group, they didn’t build off their age-25 success, because they did get meaningfully better. But instead of improving more, the players regressed. Even with young breakout players, the numbers suggest you lean on an ordinary projection...

In other words, the results are exactly what you would expect if you’ve been reading Bill James for the last 30-some years.

I don’t mean to diminish Jeff’s work. Every so often, we need a reminder that yes, baseball does essentially work as we’ve thought for the last 30-some years. But I think we can argue about the definition of “illusion”. Before 2013, Domonic Brown had a 90 OPS+, which is below average for a National League hitter and well below average for a National League outfielder. This made his 123 OPS+ in 2013 pretty surprising. Especially if you’d forgotten about his earlier success in the minors. Call it a breakout season if you will, but history suggests he won’t post another 123 in 2014. Again, forgetting about his minor-league performance, we would expect Brown’s performance to drop -- to regress, if you prefer -- in 2014.

But that’s okay. The message I take from this data is that while a “breakout season” doesn’t establish a new level of performance, it usually does establish a player as a good major-league hitter. A 114 OPS+, or 117 ... those are good. Those are guys who can play every day, make a great deal of money, and help you win a fair number of games.

The takeaway for me? Ordinary projections work, even after breakout seasons. And Domonic Brown’s a pretty good hitter. Just like we thought all along.