No rule against hitting the OPPONENT off target deliberately.
t53.2. A competitor who, intentionally, causes the apparatus to register a
hit by placing his point on the ground or on any surface other than
that of his opponent will be penalised as specified in Articles t.114,
t.117, t.120.
It says nothing about the opponent's VALID surface.
Or is this another difference between the USFA and the FIE?
It is my standard approach to fencing a certain lefty who likes to hit me on the right shoulder....being an epee fencer, I stop hit to the wrist...