The anti reversal latch is a pivoting wedge that swings against angled teeth on the bevel gear. It operates like a ratchet to prevent the gears from spinning in reverse.
If the gears were to spin in reverse, the sector gear teeth would crash behind the piston body pick-up tooth. This could destroy the sector gear teeth and piston.
In the event the AEG fails to complete a piston cycle, the anti reversal latch will suspend it in place. This may happen if the battery did not have enough charge for the cycle. That being the case, some manufacturers provide a way for the ARL to be released.