On Gray Hammer, Alpha Team, there's a box near the garbage container and the explosive barrel thing.
Then Jump on the Garbage container or explosive barrel thing, then jump on the big crate. After than go on the corner facing the alpha team. Walk back and forth until you fall in.
Bravo Team Glitch
There's a container in Gray Hammer in front of bravo spawn, you know, the one people jump on all the time.
Get on it, face the left corner closest to where you spawn and crouch, facing down, move back and forth on the edge of the corner.
Boom, you get in, and you can't be killed unless someone goes in to get you.
Credits go to timmyeo of Game Cheetah for both glitches.