Apart from the obvious, the kit worn by the teams.
I’m not sure about all the rules in American football, but in rugby You can’t tackle/hit the opposing player until they have received the ball’
The ball cannot be passed forward, has to go back.
Rugby doesn’t have two different teams offence and defence, it is the same team playing for the whole eighty minutes with a fifteen-min break after 40 mins unless one or two are substituted because of injury or just not playing well
You cannot do a high tackle, i.e. round the neck I think that’s the same in American football though.
In rugby, on the field are 15 players in each team, 11 in each team on American football field.
Also in Rugby, you have the sin bin.
The sin-bin is the bench, where all players who have committed a yellow card offence sit out of the game for 10 minutes.
If the referee believes a player has committed a serious foul or shown indiscipline, then he will show them the yellow card, just like in football (soccer)
But unlike in football, (soccer) that player must then immediately leave the pitch.
They then have to sit in the sin-bin for 10 minutes while the game continues without them.
It leaves their team a man down for a sizeable chunk of the game, giving the opposition the perfect opportunity to push for points.
If I need correcting in anything, please comment.