How come people get kicked from the games when they are playing?

I am not talking about kicking people who are killing their own team mates, but just kicking people. What are the different reasons?

There are a number of times we will just be playing along killing the other team and then all of a sudden we will be kicked from the game by the host. Just wondering why.

Maybe the person you were klling was the host and he got ****ed off.