One Minute Bunkai: Juji uke (X block) has many bunkai (applications), this example shows a defense against a straight punch to the face. The evasion is a simple body shifting to the side (Tai Sabaki) and the actions of the hands are going directly into the trapping motion. There really is no blocking in this technique. The overhand strike into the arm must be done in perfect timing with the catching-trapping hand from below.
Be careful not to confuse this with a “jodan uke” do not push the attacker’s arm up and away from you and do not side step to create a large gap between you both. The key here is to receive the punch and allow it to reach its full extension therefore do not alter its path this way it is a perfect set-up for the technique and even if the attackers begin to withdraw his arm it does not really matter because then he is helping your counter move. Once you have caught him it is a very painful lock and easy to drop him with full control. In addition the final position gives you a classic and extremely painful wrist lock.