It's obviously a best-case scenario to never have anyone lock their hands in that position, but it can happen. Assuming he gets hands locked, I thought Frank described the situation very well. It's basically pushing their head down and shrimping away to make space. In that position one thing I like to try to do is escape my bottom leg from his grasp and quickly sit-up, hopefully being able to roll over into a Marceloesque crucifix position. Basically turning his grip on your top leg into a crucifix the same way you would a single-leg. Anyway, yea, best to not let them connect their hands.