Being knocked down is done with a shove or bump often by another person. Your balance being let, you fall over. You can be shoved hard or just enough for you to loose balance. Either way, if you fall you were knocked over. It can be on purpose during a game or argument, or it can be by mistake while in a crowded area, In any case, the term is usable.

It means to hit you or push you so hard that you fall down on the ground. You could also stack some blocks or rocks on top of each other very high and knock them down with your hand.