When you're carrying the ball, you should stay near the teleporters. So if anyone tries to get you, you can just go through and hide in it and just beat down anyone that ends up on your side of the port. But watch for the other team/players to be around the other end of the port.
Also, if someone is attacking you, throw the oddball at them so they'll pick it up and be temporarily unarmed. Once you do so, you can shoot back. But watch for them to throw it back to you.