Direction Shift Boosted
A Direction Shift Boosted is when the direction of a boosted is changed when falling off a ledge. The directional change occurs before the punch-uppercut inputs and before Jak enters his falling animation. The technique is most commonly used to perform a mandatory Scoutfly Boosted during Lava Tube Skip, but it is also optionally utilized by speedrunners in other areas of the game.
Simply move the left analog stick in any direction once Jak has slow-walked off a ledge. Then, proceed with normal boosted uppercut inputs.
It is unknown who first discovered the direction shift boosted, but it is believed to parallel the discovery of the Scoutfly Boosted since this is a directional shift boosted performed on a Scoutfly crate.