Commentary
The play shows a defensive trick, catching the opponent's sword and pulling it from his hand. It is possible a self-defence advise, prima custodia being the first position you get when drawing your weapons. It also may be a solution what to do if you are not able to draw your weapons in time.
Second image shows how the attacker can release his sword by pulling back and hitting the opponent's hand with a schiltslack at the same time. This action will in fact resemble first part of pull and push action.
The text also explains that if the scholar the strikes the priest from above after he released his sword, the priest would defend by the sword and shield held together in left hand. The text also says that he will then break the shield from his hands, which is shown in the next image ... but we never get the next image. What I believe will happen is that the priest will grab the scholar's shield by the bottom part of the rim, and while deflecting the scholar's strike, will turn the shield around, releasing it from the scholar's grip.