h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I read the following on this very lovely and informative site:
'Using Shields as Weapons in Battle
There is more than one way to disable an opponent in battle. A broken leg or dislocated knee will completely prevent someone from fighting. In very close fighting, jamming the sharp edge of a large, square shield down on the extended leg of your opponent or shoving it upwards, breaking their jaw, would destroy them as effectively as a well-placed sword thrust. The shield was a very effective weapon as well as a defensive tool.' I taught this at school as I am a teacher and a fellow teacher said it was completely wrong. Please feedback.