Set via console: g_gametype <value> then map_restart. Must be set before the map command in server config files.

g_gametypeGametype
0Free For All
1Tournament (1v1)
2Single Player Deathmatch (SP only)
3Team Deathmatch
4Capture The Flag
5One Flag Capture
6Overload
7Harvester
8Elimination
9CTF Elimination
10Last Man Standing
11Double Domination
12Domination

g_gametype 2 is not intended for multiplayer. Avoid it on public servers.

Special Options

Instantgib, All Rockets, and Vampire Mode can be applied as modifiers on top of standard gametypes.