May the force be with you

since I dont watch football how would a ref call this?
'get your ass up'
or
'player foul with bad intentions'?

I'm very confused. Why do so many players do this? Wouldn't it be better to just keep playing instead of faking an injury?

If the referee would believe in the "victim", the other guy gets a red card straight.
If the referee finds out it was staged with this intension, the "victim" will get a yellow card.
It's just pretty unfair tactics and me, as a footbal fan (like really, I go to the stadum every two weeks) disapprove this af. It's boring, in most of the cases doesn't bring the effect aimed for and kills both the game and the atmosphere.

Do they really do stuff like that , in those games ??