First, hit him in between to buy yourself time. You will learn to control his foot and his structure, or he could escape. Enjoy.
We don't defend, we don't use an ellbow shield. We hit actively against an attack to open the structure for following atacks.
In order to destroy or at least disturb the structure of an atacker, you have to move before your next (counter-) atack.
Disturb the stability of the atacker, slow his next atack, break his structure again and finish with an easy takedown.
Note that the 2nd shield is not a defense, it is a hit. enjoy
Grabbing the arm during a fight is not easy. First you do not want to start with a grab, hit or block the arm, then aim for the big muscles. In a hot and humid environment or if the atacker sweats, you will end up at the wrist, like sliding down a smooth bottle.