How? The ball is still in play? Players deliberately play the ball off others in every game.
It’s a ridiculous decision. You can never have a shot on goal ever again!
Kicking the ball against a downed opponent deliberately is unsporting behaviors and an obvious yellow. The key point here is deliberately kicking it in to the opponent as a malicious act, as opposed to shooting at goal, playing a long pass etc and it coincidently hitting another player.
Obviously if it's not deliberate, it's not a yellow.
That judgement is for the referee. Unsporting behavior is a catch all, it's in the laws. Like dissent, you don't see it enforced properly. It would be great it dissent was actually enforced properly. Players whining at the ref continually ruins the spectacle and none of the refs have the stones to yellow for it when they should.