This week we reprise an action from December 2013 - the stop hit or stop cut.
In right of way weapons, the stop action must either land before the start of the final action of the attack, physically or psychologically cause the attack to stop before it hits, or hit an attack that misses. In epee it has to land within the 80 millisecond window of the attack (40 milliseconds or 1/25 of a second before to 40 milliseconds after) if the intent is a double hit, or more than 40 milliseconds before the attack if the intent is one light. Stop actions are valuable against opponents who have flaws in their execution of the attack, who have a shorter reach (both extension and lunge), who are significantly slower than you are, or who routinely miss.
Timing is obviously key to a good stop, but the mechanics of execution and footwork are also critical. You must have good blade control and be able to hit your target. You must use the full reach of your weapon arm. You must accelerate rapidly using the body part accelerations available to you - arm, torso rotation, fingers (and leg if you are attacking into the attack to provoke a double in epee). You must go directly at your target with the most efficient movement possible. Do not waste any movement, because movement is time, and time is life in the sword fight.
Footwork is also key. The traditional reassemblement to withdraw the forward foot and reach with the upper torso is still a valid technique in foil and epee, especially against the foot touch in epee. In some cases you may be fast enough to hit without footwork movement to control your vulnerability to the original attack. However, in sabre and epee, a retreat to reduce vulnerability while hitting the advanced target is a stock technique.
Stop hits are most effective if they result in one light - yours. Backward movement once the hit is secured achieves two key objectives in the one light solution. First, it adds to the travel time for the opponent's attack to land. In sabre and epee this may delay the hit enough to ensure lockout if you are stopping against the advanced target. Second, it may reduce the pressure available on the hit to less than 750 milligrams in epee or 500 milligrams in foil. The difference in both cases is going to be small, but fencing is a game of millimeters, milligrams, and milliseconds. One of one of the three millis may be enough to ensure one light.
The interesting question is what to do if you are attempting to double against the attack in epee - in this case forward movement collapses the time, and a lunge may be the answer to ensuring you are within the 80 millisecond window.