This one allows you to fly above the map for a few seconds, before coming back down, which then allows you to speed run through the map, much faster than crabwalking.
This one is hard to explain without a video, but on the Gridlock map, if you're looking towards the Sniper Spawn, then you will need to go to the left spawn point. You should see a car backed up into a 45 degree angle. Place your character into the little corner where the car meets the wall. Look straight down and throw a smoke grenade, and right before the grenade explodes, do a backwards roll. If done right, your character should rise above the map, once you get back up. Roll to go back to the ground, which will allow you to run really fast.