Counter to Armbar from Reverse Half Guard, 2on1 Sweep from Reverse Half Guard — Part 3/4
If, as you are diving under from koala guard, your opponent backsteps and lands in your reverse half guard, your arm will be vulnerable to an armbar attack. Braulio teaches how to position your hand/arm to prevent the armbar and shows how to sweep from there as well. This is applicable if your opponent's hips are on top of you.
Links to other Parts:
Part 1,
Part 2,
Part 4