Is it possible play free-for-all in LAN games?
Solution 1:
You can do that with mp_teammates_are_enemies 1. This will turn your allies as well as your enemies into valid targets.
If you're in a local game you can just enter this in your console. On a server (LAN or Internet doesn't matter) you need to prefix it with rcon (and be logged in with the rcon password):
rcon_address server-ip (not needed when you're currently playing on that server)rcon_password ****rcon mp_teammates_are_enemies 1