Also known as: Achilles Lock · Footlock · Botinha · Straight Foot Lock · Ashi Hishigi
The entry-level leg lock and still an elite finish: blade of your wrist under the Achilles, foot trapped in your armpit, hips arching through the ankle.
Submission · Ankle Lock · Gi & No-gi · Difficulty 2/5 · Usually learned at White belt
Starts from Single Leg X as the slx player → ends the match (submission).
The details that make it work
Trap the foot deep in your armpit; your wrist bone sits under the Achilles, not across the toes.
Knees pinch their leg; your outside foot stays OFF their far hip in IBJJF (crossing to the far hip is a DQ at lower belts).
Finish by arching hips forward and up, chest proud — a bow, not a lean-back yank.
Where it goes wrong
Falling to the wrong side (toward their free leg) where their knees pummel you off.
Sawing the forearm without hip extension.
How opponents counter it
Free the heel by "putting the boot on" before the grip sets
Come up top and stack through the lock
Is the Straight Ankle Lock legal in competition?
Legal at all IBJJF belts (the classic exception in a mostly-restricted leg lock rulebook) — but crossing your outside foot over their far hip while attacking it is not. Legal everywhere in no-gi and sub-only.