Examining baseball’s star player turnover

The are a lot of theories as to why people are and have been attracted to baseball: a sense of community, plain ‘ol fun, and the sense of the ephemeral. The latter is strange, but it makes some intuitive sense; if you know that this is the only time you’ll see a player this great, or a particular play like that, or a memorable moment, it means you’ve cemented yourself in a moment that can’t be replicated. People order the meaning of their lives on nostalgia and memory collection, so it’s fitting that we center our meaning of sport around the same principle.

If you were to rewind five years, what great players do you remember watching? Ten years ago? Fifty? Each year backwards becomes more different, distant, and fuzzy than the last, and that’s because—once again—like life, the team’s best players are as ephemeral and shifting as any moments in your own life.

Take, for example, the top ten players by fWAR in 2013:

Of these, how many fit into your top ten today? Mike Trout, obviously. Matt Carpenter, but circutiously so. And possibly Paul Goldschmidt, but that’s really how much you weigh his first half.

Which means that the relationship between then and now is almost... tenuous:

Only about 15% of today’s performance of top players attributed to their performance five years ago makes sense in a way; this is why projection systems usually take multi-year samples to bump that number up. What I’m more talking about is if we took a snapshot today, the definition of the ephemeral, and then flash-forward, what does that look like? It’s a time machine.

When you go back ten years, as I said, it looks even more different:

One is already in the Hall of Fame, with two shortly thereafter. Of those, five are already out of baseball, and two are still working back from injury. So, yeah, the relationship here is going to be non-existent to what they produced in 2013...

...as well as today:

It’s just something to keep in mind when you’re watching, albeit this is a much younger group of stars, so my inclination would be the relationship is slightly stronger: the players who wow you today almost certainly won’t be doing that a half-decade from now, and they will be gone before a kid born today reaches middle school.

What’s even funnier is when you think about relievers, as well, and then things get accelerationist: not a single one that was in the top ten of reliever fWAR in 2017 is in the top ten today. This was also just written about at FanGraphs: compared with position players repeating 3+ WAR seasons 40% of the time by year 3, relievers only repeated 1+ WAR seasons 32% of the time. That still says that about a third of relievers are still “long-term” pieces, but long-term in the sense of a contention window. Hey, if you have a busy three years and miss some baseball, you’ll come back with a top relief corps that is ²⁄₃ completely different.

This is only a Fun Fact exercise, but it serves the purpose of trying to appreciate players in the here-and-now, because there’s a good chance you’ll only get to watch them in their current form for a, tops, 3-5 year period. As much as baseball historians like to think of the sport in “eras,” the time that the sport is defined by its best players is only the blink of an eye.