It was probably in Tribes (with the renegades mod). I was playing as an engineer on rollercoaster (don't let the name fool you, it was actually a heavy sniper). After going through the trouble of lugging a deployable station all the way to the outskirts of the enemy base, I started sniping. Eventually someone who just spawned tried to come and kill me but thankfully I had a rocket launcher. I took his energy pack, grabbed some health and ammunition, and then continued sniping and fending off close assaults. By the end of the game I had scored 59 kills without dying a single time.