You’ve got it a bit backwards. The question should be, “Why did football evolve to have entirely separate personnel for offense and defense?”
Football originally featured the same players on both offense and defense. It’s actually pretty recent that it changed - around WWII. Due to the war, there came to be a chronic shortage of players, so true Ironman football was no longer viable. Free substitution came into being and teams with dedicated offensive and defensive squads came into being. Technically, you can use the same players for the entire game, but there’s just no way they’d be able to compete with teams that substitute.
Baseball never really had that problem. With the exception of pitcher, you can play the same players inning after inning and game after game without too much trouble. Baseball players shouldn’t get so tired they can’t both bat and field (except, of course, the pitcher). And there’s not really a problem finding players who can do both at a high level for 9 innings. Likewise, soccer and rugby are still largely the same, featuring limited substitutions.
Yeah, American football is pretty much unique among in having two separate squads. Sure, you can what-if it, but if you’re going to make changes that big, why stop there? I can think of hundreds of ways that you could change the sport of baseball, and for every one of those changes, we could also ask “why not?”.
I hope it never happens to baseball, except, and I know I’ve posted this before, for the all-star game. It’s an exhibition so let the best hitters bat and the best defenders play the field.
While I’ve come to accept the DH, this would be an awful rules change for baseball. Sure, it’s maddening at times when you’ve got a good catcher or shortstop that can’t hit, or someone playing first who’s a good hitter but fields worse than an intoxicated sailor with cataracts, but that’s part of the game.
Football allows free substitutions, so it’s natural for separate offensive and defensive squads to emerge. It’s just a matter of subbing in the best players for the game situation.
In baseball, once a player is substituted for, he can’t come back into the game, so you can’t have separate offensive and defensive squads without a major rule change.
Cricket has a standard 11 players for both fielding and batting, players can only be changed in very limited circumstances when fielding and not at all when batting (apart from runners).
I know next to nothing about American Football, but this doesn’t seem to make sense - there was a chronic shortage of players, so they solved this by doubling the size of the squad?
Shortage of players of a certain age, at least. Back then, many of the upperclassmen were off to war, often leaving many younger players, who couldn’t keep up for 60 minutes with teams that may have still had a full complement of older, stronger, more experienced players. Free substitution and specialization gave them a chance to compete. Those teams may have only had 4 or 5 older players but enough underclassmen to field a couple teams.
For baseball, a team of underclassmen may not have been able to compete with upperclassmen, but it would be surprising if they couldn’t at least finish the games, as would be the case in football.
That does lead to problems in peacetime when teams can freely substitute not with a bunch of leftovers but with top-notch talent and the sizes of teams have to be nearly doubled to compensate. Purists wanted to go back to ironman football (playing both offense and defense). But it was too late to put the genie back in the bottle.
Incidentally, it’s things like this that make me laugh at American football ‘purists’ who complain every time a rule is changed. The history of football IS rules changes every few years, and often with a lag or persistent differences between college and NFL rules.
But, as noted, the default for many sports has been limited substitution. And that’s fine. Many sports might be different but probably wouldn’t be significantly improved with free substitution. And those that would already allow it, like basketball or football.
I think the point was not that teams couldn’t find enough players, period, but that teams had fewer experienced players, who were more capable of playing a full game. What’s not clear to me is whether the change in the substitution rules during WWII also coincided with an increase in roster sizes.
This digest of NFL rule changes indicates that the NFL got rid of free substitution in 1946, only to re-implement it on a trial basis in 1949, and then on a permanent basis in 1950. It looks like the NCAA’s change back to full substitution may have been more gradual.