MLB Debuts, by Season and Franchise

As the truncated 2020 regular season wraps up, it’s a good time to take a look at some of the trends that this unprecedented seasonal format has given way to. Among all these changes it is easy to overlook that, for the vast majority of professional baseball players, 2020 was a lost season. For some young players though, 2020 meant spending time at alternate training sites and getting looks from team executives that they might not otherwise have received; in some cases it meant earning a Major League promotion, too.

So to put just a fragment of 2020 into some context, Baseball Reference data have been drawn upon. The following delves into the number of Major League debuts this season and juxtaposes those figures to similar ones over the past decade. Spoiler: 2020 featured a wildly outsized number of MLB debuts.

The chart below illustrates the number of debuts in each season dating back to 2011. You’ll notice that every year 200-some players (239 on average) earn the promotion of a lifetime.

In a sixty game season (that is still unfinished), 204 players, or 3.4 per game (across all 30 teams), have made their MLB debuts. The next closest figure came in 2017 when 1.62 debuts were made per game. Interestingly, despite more players making debuts per game in 2020, there doesn’t appear to be explicit evidence that those players were “rushed” as measured by their average debut age, which is squarely in line with years prior. In a game where the majority of those players getting playing time are younger than before, average debut ages remain predominantly consistent over the last decade.

The arc of each seasonal cohort’s cumulative bWAR is also a bit interesting. 2011 of course comes with the most MLB tenure amongst those listed players, but it was a stacked group nonetheless. Mike Trout, Paul Goldschmidt, José Altuve, Anthony Rizzo, and Kyle Seager all make the Top 10 list in career WAR to this point; while some of those names will inevitably drop out of the Top 10 as other players reach their primes, not all of them will.

Finally, it should be noted that while the maximum age for players reaching the Majors in any given year might be unexpectedly high, that number is boosted by international players transitioning leagues. Of the 10 oldest players to debut since 2011, 9 of them were born internationally and signed as international free agents.

Next, data has been aggregated by team, rather than by season. While average debut age is rather smooth across the past decade, there is a bit more variation between franchises.

There are several glaring caveats to a table like this one. First, many players are still (or really, only just) accumulating WAR. Second, teams who promote a player are given “credit” here in bWAR for everything he accomplishes thereafter. The Houston Astros have a huge total, but J.D. Martinez is responsible for a portion of that sum; all the bWAR that Anthony Rizzo earns has been attributed to the Padres, etc.

More interesting, in this blogger’s opinion, is that there is a weak (-0.07) negative correlation between the number of team promotions and the WAR of those players promoted. In short, quantity does not beget quality. In fact, given that most players to reach MLB are still hard-pressed to accumulate any significant WAR total, more players being promoted very likely dilutes any sort of WAR/promotions figure on a team basis. Finally, it should be noted that both the Athletics and Rays, two teams rightfully esteemed for both developing and acquiring players, have promoted some of the fewest players and some of the oldest on average.

This final table is a replica of that above, but filtering to include only debuts from 2020 (through September 22nd).

This table depicts the aggressive tactic of some teams in promoting organizational players this season (Marlins, White Sox, Cardinals) versus more cautious organizations (Cubs, Angels). That number might be a function of a team’s quality and progressions of prospects though, too. Altogether in the case of half of these teams, rookie contributions have been negligible or negative. Still, some teams have benefitted from their graduated cohort. Luis Robert, Ryan Mountcastle, and Jake Cronenworth jump out as players who have benefitted their respective teams.

It’s probably inadvisable to speculate and project even what this relatively minute aspect of 2020 will mean for players going forward. Some players were probably rushed; some may have nerves that benefitted from empty stadiums, who knows? Those players who weren’t fortunate enough to make it over from the alternate camp, or be invited to alternate camp in the first place, will have a strange path ahead of them going into 2021. Despite that fact, or maybe because of it, it is encouraging to see that roughly the same number of professional players had the chance to make the Majors in a year when nothing has gone as planned.