Well, maybe it was dark. The shadow of a plastic video game gun might look like the real thing.
As reported by the Pittsburgh Post-Gazette , a 24-year-old man fended off an intruder with a gun he was using to play a game.
The Oakland man (the town of Oakland is part of Pittsburgh; we're not confusing it with the California city) says he was playing games when someone knocked on his door and asked for a person he didn't know. The guy said he felt threatened, and he wielded the prop gun to keep the intruder at bay until the police arrived. We don't know what type of gun he was using or the name of the game, but none of 'em would fool you into thinking they're real.
That's only if you could see them well enough, though. So, maybe it was dark, or the guy never saw him through the door. Either way, yelling "stay back, I've got a gun!" is probably at least somewhat effective.