I agree with grappling rules being to complex and/or being hard to understand. But the system I would have would almost be like a stamina gauge in a videogame where if ur holding onto the guy tryin to take him down for 30 seconds or a minute and don't get it he's gonna be able to do whatever he wants to you until you rest. with the way I'm thinking of it your going to have a few different types of grappling one would be for taking someone to the ground, where you would have simple tackles, slams, trips, and judo throws for example. Than when you were on the ground it would be a different system you ere using instead if the guy on the bottom just defending against your grapple he would try to counter it with a submission or (if they have enough skill) sweep them you would have other options as well depending on on your style (class), size and gym.