Often in science fiction you see a force field protecting something. The heroes shoot at it just to establish that it's really there, and the energy blasts or bullets seem to be absorbed or disintegrated. So I started wondering what would happen if the force field reflected anything you propelled at it right back where it came from. Throwing a rock would be a bit of a bad idea, but shooting such a force field would be like shooting directly at yourself. Makes for a much more effective defence, in my opinion.
Mokalus of Borg
PS - The good guys should be in control of such a force field first.
PPS - Otherwise good guys die just finding out that the force field is there.