This is another way to damage the arm. And to come to other plays and locks, I start with this play. Also I say that if I were caught by a spear, with such a strike I would either unpin myself or break the head from the shaft.
Although the application here is slightly different, the mechanics at play are the same as those used by the 5th Master. As your opponent grabs you, move your left arm so that your elbow is on your hip and your forearm is horizontal. Rotate your hip slightly clockwise so as to chamber your right hip. Grab your left wrist with your right hand.
Keeping your left elbow reasonably still, rotate your left forearm around to strike against your opponents elbow. Use your right hip to drive forward, simultaneously punching with your right hand and adding that force to the movement of your forearm. You will be in a nice Tutta Porta di Ferro Dopia.
You will hyperextend and damage your opponents elbow by doing this. How much damage is done depends largely on your opponents grip. If their grip is immovably locked into a grab, you should inflict a large amount of pain. At the very least, you will knock their hand free and turn them slightly. Either way, you will be left holding the initiative while standing primed to attack on their outside line.
Fiore notes that this will also work against a spear thrust which may have caught in your (presumably very thick) jacket or armour. Using the same mechanics in a different context, you can either knock the spear aside or potentially snap it altogether.