This is a strike that was favoured by Defense dans la Rue instructor J.Renaud and one applied, to various degrees, by English and American boxers.
Best deliverd at close range, the chop blow can produce knock out potential at a distance in which other punches are ineffective or, at best, achieve a pushing action.
The chop blow should not be confused with another strike common to the older methods of classical English boxing called the ‘chopper’. As recommended by Renaud the chop blow travels along an oblique descending trajectory using the hammer edge of the fist to strike with. The path in which the chop blow takes, carry’s it outside the adversary’s peripherals prior to its return into the target. This makes it very difficult for the enemy to visually track, by the time movement has been detected he’s already been hit.
From “Boxing For Beginners” 1918 –
“Illustration shows the chop. This is sometimes a useful blow. Use the fist as the head of a hammer, the forearm as a handle. Especially effective against opponent who rushes in with head down”.
The late Carl Cestari provides an excellent break down of the chop blow in this Youtube clip-