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It’s good to be young

Baseball’s 23 and younger class is small, but potent.

MLB: Seattle Mariners at Boston Red Sox Bob DeChiara-USA TODAY Sports

McCovey Chronicles will be covering news from around the league all season long with our new daily MLB Chronicles column.

You already knew that younger players are the coin of the realm and the foundation parts of every successful team. Competitive windows are opened by the youth and kept open by the veterans.

We might not know what a veteran is anymore, though. In this new era, the aging curve is a cliff and there’s nothing graceful about the fall. Rookies are seemingly getting fewer and fewer reps in the minor leagues and debuting at younger and younger ages. More importantly, these younger players are sticking when they get the opportunity.

At least... that’s certainly what it feels or seems like. But what does a bird’s eye view of the data say? I’m going to focus on just the hitters because 1) it’s more fun and 2) pitchers do tend to both improve as they get older and still have the ability to produce in the current climate after age 33. For now, anyway.

There are 19 players aged 23 or younger who have made at least 50 plate appearances so far this season. This accounts for 5.4% of all players with at least that many PAs. This group, led by Cody Bellinger (4.2) and Ronald Acuna Jr. (1.9), has a combined 15.3 fWAR, or 0.8 wins per player.

Compare this to the other end of the range: those cagey veterans / 34+ year old batters. 37 such players have 50 or more plate appearances so far in 2019, accounting for 10.5% of the list of players who have at least that many PAs regardless of age. This group has combined for 8.5 fWAR or .229 per player.

We’re dealing with a very small sample of eight weeks into the season here, though, so that disparity, while jarring, might not tell the whole story. I mean, can sub-24 year old players really be the key to unlocking team success?

Seventeen teams have produced that field of 19 batters. The Padres lead the pack with three (Fernando Tatis Jr., Franmil Reyes, and Francisco Mejia), while the Dodgers (Bellinger, Alex Verdugo), Braves (Acuna, Ozzie Albies), Red Sox (Rafael Devers, Michael Chavis), and Nationals (Juan Soto, Victor Robles) all have two.

The Royals (Adalberto Mondesi), Nationals, Blue Jays (Vladimir Guerrero Jr.), Mets (Amed Rosario), and White Sox (Eloy Jimenez) are the only teams of this group with sub-.500 records. Three of these teams are “rebuilding”.

Compared to the rest of the field (297 players aged 24-33), the 23 and unders are sporting a nice WAR per player efficiency (24-33 grouping is 0.5 per player), but again, the sampling is ridiculously small and top heavy thanks to Cody Bellinger’s morally wrong start to the season. How have these groups sorted out over time?

First, let’s jump back ten years to see how it all looked:

WAR per age bracket, 2009

Age fWAR # of players (% of 50+ PA) fWAR/player
Age fWAR # of players (% of 50+ PA) fWAR/player
23 and under 43.7 49 9.0% 0.87
34+ 67.8 73 13.5% 0.93
24-33 476.9 419 77.5% 1.14

That’s about what you’d expect if you thought that a decade ago, the prime players would be the biggest contributors and players 34 or older would still be able to provide above league average production. Now that practically every pitcher can throw 94 mph+, it’s been harder for these players to stand their ground and produce at a similar rate. Or is that just what we think? Does the data support that?

WAR per age bracket (2009, 2016-2019)

Year Age fWAR # of players (% of 50+ PA) fWAR/player
Year Age fWAR # of players (% of 50+ PA) fWAR/player
2009 23 and under 43.7 49 9.0% 0.87
2016 23 and under 75.3 54 10% 1.39
2017 23 and under 47 58 10.6% 0.81
2018 23 and under 42.9 56 10.2% 0.77
2019* 23 and under 15.3 19 5.4% 0.84
2009 34+ 67.8 73 13.5% 0.93
2016 34+ 40.4 47 8.6% 0.86
2017 34+ 27.8 53 9.7% 0.52
2018 34+ 44.6 55 10.0% 0.81
2019* 34+ 8.5 37 10.5% 0.23
2009 24-33 476.9 419 77.5% 1.14
2016 24-33 471 441 81.4% 1.07
2017 24-33 508.4 435 79.7% 1.17
2018 24-33 495 439 79.8% 1.13
2019* 24-33 150.3 297 84.1% 0.51

What you can see here is that the notion of a crafty veteran still having value has rarely been true. While the percentage of PAs given to 34+ year olds in 2009 is slightly higher than the rates just seven years later up through until today, we’re still talking about less than 15% of the baseball population (minimum 50 PA) hitting in their mid-to-late-thirties. As a group, this performance has fluctuated wildly in just the last couple of years (Albert Pujols and Chris Davis, especially, have helped pull down the numbers).

Meanwhile, the idea that a youth explosion has overrun the game doesn’t quite hold up, either. The rate of sub-24 year old players has remainined steady around 10% and their typical WAR contributions, on average per player (an obviously rough and problematic approach to examining the information), have remained right around that 0.8-win area.

Mookie Betts (8.3), Corey Seager (6.9), and Manny Machado (6.3) had everything to do with that ridiculous 75.3 fWAR outburst from the 23 and younger set in 2016, and that’s really the punchline: put great players on your team and your team will be good. Draft and develop generational, preternatural talent and you will be rewarded with production that looks simply obscene on the page.