I put my shin to the opponent's thigh, take the underhook by grabbing his shoulder, sit out and pass the guard. Make sure you stay tight and push his arm with your body. My main purpose here is to get his arm out of the weight, controlling him with the underhook from the one side and my hips from the other, I throw my leg leg over and trap his arm. If you have a chance to grab his wrist and pull it, you'll have even more control over his arm because you'll have it extended more. Now he can defend himself only with his free arm. I grab him by the wrist and push it. I have much better leverage here, it's almost like bench press here. Once I push his wrist forward, I get my head through and end up in the crucifix position. Important point, the higher you swing up, the heavier your punch will be. Some people think it's better to use short punches from this position, but this big punch is really effective here. You can use various elbow strikes here as well if they are legal. Make sure you always keep the control of his arm with your legs. If he gets his left arm out, just keep holding him with your elbow on his hip and with your hand on his shoulder. Stay on him and look for the opportunities. You can follow up with the submission or trapping his left arm again and throwing strikes on him. Again, big punches are really effective here.