You have the Side Mount (aka Side Control). Now, you have to keep that position. Your attacker is not going to be to happy with you in that position, and may try to roll you off. If you don't know how to stop this rolling, they will get you off of them!
So, from the Side Mount, if they roll in the direction of your "underhook", ie, your arm that's under theirs, you post that arm out. Reach out and plant the palm flat out on the ground.
If they decide to roll the other way, you push from your posted leg, where your sole should be flat on the ground. Incidentally, when they do roll that way, and you push from your posted foot, remember to bring your posted HAND back, clasped onto the neck-hugging hand. Why? It's because it will keep you in tight, and close, and you're able to put more of your body weight on them.
This is a very effective way to maintain the Side Mount on a street attacker who is unfamiliar with the position and is trying to throw you off.
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