Artemis BJJ (Easton Road), Can Sönmez, Bristol, UK - 11/03/2020
First you need to isolate their near arm. The old school method is to dig your knee inside and open it out towards their head, but people will often be wise to that and keep their elbow in too tight. The method I use is to grip their elbow, turn my hip to the mat, then scrape my hip bone along the mat. The idea is to scoop up their arm through a combination of driving presence from my hip (powered by your legs, walking up to their head) and lifting the elbow with my existing hand grip.
Stay tight, walk up high to their head, then turn your hip back down to trap the arm. Reach your arm through, then pull your elbow back to trap their forearm and wrist in your armpit. Your leg nearest their legs curls inwards, tight to their side. Bring your other leg over their head, making certain everything is tight: so, pull your heel in close to their skull, scooting your but forward as close to their shoulder as you can.
Your knee nearest their legs pops up, with your foot tucked underneath them (though if possible, you can bring that leg over to get a stronger position). To control from that position, squeeze everything in tight, so knees together and firm grip on their arm. From here, you may be able to lean back for the submission, if you have their arm properly configured under your armpit. If not, control the wrist and adjust into a more standard grip, drop back, pull down on the wrist and lift your hips.
Teaching Notes: Popping you knee up is key, as always. Also getting your heel close to their skull and your bum in close to their shoulder. As with all armbars, people leaving space is invariably the big reason they have trouble with the technique.