Rugby, (American) football, and soccer have common roots. So can anyone explain why in both (American) football and football (soccer) there are 11 players on the field for each team while in rugby (at least rugby union) there are 15?
To make it more intriguing, Rugby League has 13 players. I have no answer to the original question other than it is tradition.
And, Canadian football has 12 on a side.
The Wikipedia article on American football indicates that the game started with 25 players per side, and over the course of the 1860s and 1870s, it was gradually lowered to 20, then 15, and then to 11 by 1880, when Walter Camp codified a set of rules for the game.
If you go all the way back to medieval football, there were an unlimited number of players per side.
The very earliest official Rugby Union games in the 1870s were played 20-a-side (mostly forwards). It was reduced to 15 in 1877 to encourage more open play (and make it less of a mass wrestling match with a ball stuck in the middle).
Rugby League subsequently eliminated another pair of forwards for the same reason, going from 15 to 13.
I suspect all the Rugby-type games evolved from “all of us vs all of them” free-for-alls where the ball was mostly used as an indicator of which side had managed to shove the other off the field. Actual ball skills came later.
Okay, I found website that tell when Association football, rugby, and (American) football adopted rules:
{here}:History of Association Football (Soccer) From Early Beginnings To Present
{here}: Rugby Football History
and
{here}: History of The Game Of Football Including The NFL and College Football
respectively.
Only for Association football did I find something that (may) explain why the # of players used is what it is, though: https://www.quora.com/Why-is-football-played-with-11-players-Any-logic
Because things evolve. They may have common roots but then they became different sports. Each sport had its own reasons for making changes to its rules. The fact that both American football and soccer have 11 players is just coincidence.
BTW I think organised football might be older than people think. Present day rules go back in unbroken traditions to the mid 19th century but that doesn’t mean they were the first sets of rules. I saw a reference somewhere to a 6 a side match in Scotland before the 19th century. I think it might have been George MacDonald Fraser’s book about the Border Reivers.
Rugby banned blocking around the same time.
That appears to be the case, yes.
The impression I’ve gotten is that that’s one of the big things that rugby players trying to transition to football have to get used to.
I think the other big difference is the lack of offside when the quarterback passes forward. The forward pass itself isn’t so innovative, it’s much the same as a more pinpointed halfback’s kick. But if you applied the rugby offside rule in American football, nobody would be allowed to receive the ball from the QB’s pass.
(In rugby the receiver basically has to begin from behind the kicker and run past him as the ball is kicked).