It was my initial intent to write something about Tuesday’s trade rumor that involved Domonic Brown and Jose Bautista. The rumor, presented straight-up, was absolutely fascinating for the implied processes and implications. But, two things: Firstly, Dave wrote a couple thousand words on the rumor, touching on a lot of what needed to be touched on. Secondly, the rumor was thoroughly discredited Wednesday. That’s not to say the teams haven’t had talks — which isn’t to say such a deal is impossible — but it’s pretty evident nothing’s going to happen soon. No sense writing more about something that’s purely hypothetical.

But something within Dave’s post grabbed my attention. Brown just had himself a breakout season at 25 years old. The way we think of these things means Brown has achieved a new level, and going forward he’s going to be an excellent hitter. Dave presented a few counter-examples — young players who had breakout seasons in 2012 before largely taking a step back. The suggestion is that breakout seasons might not mean what we think they mean. Dave’s sample size was woefully small, but I wanted to dig a little deeper. It was a point potentially most intriguing.

It’s not easy to go through the recent history and isolate breakout seasons. Doing so requires a lot of time and a handful of judgment calls. What’s going to follow is incomplete — I’m sure I’m missing a bunch of breakout seasons — but the way I decided to do this was to fit criteria around what Brown has done. Research made liberal use of the Baseball-Reference Play Index, and for that reason you’re going to see OPS+ cited, instead of wOBA or wRC+. While I prefer the latter two, we don’t need that kind of accuracy here, since OPS+ should give the same ideas. All I care about are general trends, and even raw batting average would probably get the job done to a considerable extent.

Brown just completed his age-25 season, posting a 123 OPS+ in 540 plate appearances. Through his earlier seasons, he posted a 90 OPS+ in 492 plate appearances. That’s an OPS+ improvement of about 37%. That’s what a breakout season looks like. I decided I’d focus on breakout seasons at the age of 25. I set a minimum of 500 plate appearances, I set another minimum of a 110 OPS+ and I went back 50 years. This gave me a list of candidates to narrow down further.

From that list, I looked for players who, before their age-25 seasons, batted at least 400 times, and posted an OPS+ below 110. Once I had that, I honed in on just the players whose OPS+ figures improved at least 20% at 25. That’s an arbitrary cutoff, but I feel like +20% adequately describes a breakout. On average, out of my sample, the players improved in their age-25 seasons by 39%. The final step was taking these players and seeing how they did in their age-26 seasons. For those I set a minimum of 250 plate appearances, doing what I could to keep the sample size decent. In all, the sample pool has 70 players.

Here’s a complete table of the relevant data:

You’ve got OPS+ before age-25, OPS+ at age-25 and OPS+ at age-26. Obviously, within the table, you’ve got guys who got better, guys who got worse,and guys who stayed the same. What’s most important are the averages. And, well:

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, that takes more than one season into account.

This is obviously a limited and somewhat arbitrary way of looking at this. As with all of my projects, this could be researched more rigorously, with a bigger sample and better statistics. My hunch, though, is all the results would look pretty similar. We probably believe a little too much in what we perceive as young hitters’ breakout seasons. Every case is different, and maybe in Brown’s case he got better as a result of mechanical tweaks, but I bet almost all these players got better as a result of some kind of mechanical changes. As a group, though, they didn’t keep getting better.

Naturally, some did. Carlos Delgado entered his prime. Edgardo Alfonzo peaked at 26. Edgar Renteria also probably peaked at 26. On the other side, Pat Burrell got a lot worse after getting a little bit of MVP support. Carlos Quentin came undone. And the face of phony breakouts has to be Adrian Beltre. In 2004, Beltre was one of the best players in baseball, and it looked like he’d finally put everything together. He was at 26 what he was at 24, and 23 and 22. Beltre has blossomed into an excellent hitter again, but he hardly built off his breakout. It was as if his breakout never happened.

This study is far from conclusive, and maybe a better researcher will put together a better research project. I’m aware of my own limitations, and I encourage further work. What I choose to believe today, though, is that as a group, we put too much stock in younger-player breakouts, just as we probably put too much stock in older-player collapses. We think they’ll be better indicators than run-of-the-mill projections, but those projections are pretty good because they never forget that you need more than one year of information. In select cases, maybe it makes sense to look only at the most recent season. I don’t have a lot of trust that we can identify those cases. Turns out big improvements tend to be followed by regression. That’s how it pretty much has to be, even if a player’s just 25 years old. I was surprised by these results, but I’m pretty sure that’s my fault.