Best comment from the thread here.
In 1994 an English homeowner, armed with a toy gun, managed to detain two burglars who had broken into his house while he called the police. When the officers arrived, they arrested the homeowner for using an imitation gun to threaten or intimidate. In a similar incident the following year, when an elderly woman fired a toy cap pistol to drive off a group of youths who were threatening her, she was arrested for putting someone in fear. Now the police are pressing Parliament to make imitation guns illegal.
I don't fault anybody for deciding not to attack an armed man -- that's a call you've gotta make under the circumstances. But it takes a special kind of cowardice for a young man not to step in to help an old guy who's already gotten the gunman in a headlock, wrenched his gun away and is bashing the robber over the head with it.