Passing half-guard 1:
1) Underhook their arm on the SAME side as your leg is trapped, use your other arm behind their neck. Grasp hands together to lock your control.
2) Get your weight on them, and control the head – push it to the same side as your trapped leg.
3) Stretch them out and keep your weight down as you lift your knee to pull your leg out
4) If it gets trapped, use your other leg to push their knee out of the way
Passing half-guard 2 (if he has an underhook):