Huh, that's interesting. It was always a fun thing to do, but I didn't realize it was exploitable to that degree.
Here...
http://www.youtube.com/watch?v=BrArnwyKxmY <--- 480p max resolution, should be fullscreened
Alien Vendetta Map 6, the Ultraviolence maxkill record - - the map is meant for you to use infighting at the optimal times. There is a time when you will see the player switch to fists, run behind some mobs and swing into the air and move out of the room, and then a moment later come back in and circle without firing - - that's all infighting related. Infighting gets used again later in the run too, that's the first big time tho.
The player who made the run is Anders Johnsen who is well among the best in the world at speedrunning and also deathmatch.
--BahdKo