if you're referring to COD4 or CO
W@W, then yes, you must be host to lag. If you're host it freezes them, and if you're not you just get the "connection interrupted" message. You're the host if you're the only person in the game, and then others join. Also, it may migrate you to host if the other host leaves. You can make sure you are the host by just flipping your switch. If people freeze, then you are.