As the opponent reaches in or throws a straight punch, you move forward and diagonally to the right, stepping through with your rear foot (normally the right) and ending up facing the opponent while he is still facing the place where you were.
Your left hand remains ‘inside’ the opponent’s arm, while the rest of you is now outside it. Your left arm traps the opponent’s arm by raising your hand as if trying to point your thumb over your shoulder.
Drive forward with your right elbow, pushing it sharply through the opponent’s trapped arm, and drive forward with the right hip as well. This forces his elbow against its range of motion and can break it.
This position is used in a lot of control and restraint systems, and can be used to disarm an opponent if necessary.
Even if your counter does not break the aggressor’s arm, you can get him under control by rotating to face the same direction he is and pushing down on his elbow and shoulder while pulling his arm upwards.
Tactical ‘Y’
This move makes use of the ‘tactical Y’ concept. Moving up one of the arms of the Y will take you out of the threat zone.