This is something I’ve seen a few times in football, especially at grassroots. Most common case of it happening is when a defender is shielding the ball to go out for a throw in and a frustrated attacker just charges him. No play for the ball, just an attempt to floor the opponent.
Its forceful, but not excessive. It’s aggressive, not violent or brutal. Player on player that gets a yellow most of the time, sometimes it’s a red but it would take more circumstances to be a red. The case in the original situation isn’t a red, it’s a yellow for me. If its a yellow for player on player it’s the same for player on fan.
Not criticising any ref that goes red here, I can see that, although I’ve never seen a red given for it.