1. When your kata "clicks" (you're successfully grabbing enemy), you need to press direction button. Forward (arrow up or W in most cases) is for "punching" one, than send enemy forward at the end. Backward (down arrow or S) is the kata you're looking for (tm). left or right is the "strangling" kata.
2. For kata to initiate at all, enemy need to be immobile, straight ahead of you. Most of the time, he will manage to run (unless it is a sold who was just thrown to the floor), unless your opponent made huge mistake - so, kata is high risk-high reward move.
3. You can somehow mitigate that risk, if you know that changing weapon during "failed kata" animation (when you know that you haven't caught enemy) allows you to move again, without waiting for the animation to finish.
Cheers,
/Cat Lady
