stamina (yes, really), cant go over a certain speed or else you'll get reduced down to walking speed, 64 tick making your jumps not work, no spacebaring like in Quakes.
you need well timed jumps (bind jump to mousewheel down) and the jumps can fuckup randomly if you're playing on a 64tick server (what the matchmaking is) instead of 128 tick
you also have to strafe and gain speed after every jump because it slows you down if you're going above the running speed