Plutonium

When a player joins my game they are on the same team as me. How can I switch? Is there a command i can put in console?

So I make a game of greif on black ops 2 zombies. My freind joins my game through the freinds list. But he is on the same team as me. How can he go to the other team so I can actually play greif. Is there a command I am missing?