Half guard, top
Half Guard to Side Control
Flatten them from the top of half guard with a crossface and an underhook, free your trapped leg and settle in side control.
Step by step
Crossface and underhook
From the top of half guard, put your forearm across their face to turn their head away, and dig an underhook so they can't come up onto their side.
Flatten them
Drive your weight through your shoulder until their back is flat on the mat.
Free your leg
Push their top knee down with your free foot or knee and pull your trapped leg out, keeping your chest on them the whole time.
Settle in side control
As the leg comes free, slide your hips to the side, knees tight to their hip and chest across theirs.