A guy in California has actually patented a phaser that can stun from a distance. The UK defence forces are interested.

[Update at 2:57 PM PDT]

I should add, that I don't think it will work. The ability to transmit a charge through such a "tunnel" has been demonstrated, but I think that it's unlikely that it would reliably "stun" an individual. It would need a lot of power, which means a heavy battery pack, and even then, the effects on human physiology would be unpredictable. It might render him unconscious, it might kill him, it might make him mad. Life's not like the movies...