From AmtWiki

Wounds may be inflicted by contacting a Hit Location with the Strike-Legal portion of a Weapon. Shots from Melee Weapons fall into two broad categories:

A valid slash must be percussive (contact with an audible pop) and stop on or deflect off the victim.
A valid stab must strike with the tip and stop on or deflect off the victim.

These requirements do not apply to projectile weapons. Any contact from the Strike-Legal portion of a projectile weapon will cause a Wound unless otherwise noted.

Some contacts which partially fulfill the above criteria are listed here as examples of invalid shots.

Examples of Invalid Shots

Slashes that are neither percussive nor stop/deflect.
Draw Cuts
Stabs which fail to strike with the tip. These contacts slide against a victim instead of impacting cleanly.
These contacts are pushed into or slid against a victim after the initial motion was completely blocked and the initial motion had stopped.