B
Yeah, there's a sniper map that uses a command to force everyone to change class to sniper.
Don't know if there's a way to make it work in reverse to let people be anything but sniper.
Thats a good question actually, and I have also been wondering if theres some in-built way to limit classes. On my map I am afraid of a scout rushes galore, but I dunno of any way to limit each side to say 2 scouts.
If there was such a limit system in place though it could easily be used to make it so you could not join any class but the one you wanted for the map.