Tunnel beacon

An old technique used on some Renegade Multiplayer maps, tunnel beaconing often resulted in kicks or bans on the server. The technique: Some maps have tunnels close to enemy structures. All they have to do is place a beacon. They don't know where it is, and the beacon destroys the structure. This is ruled as unfair, as there is no known counter, and if a team decides to do it as a whole, impossible to stop.