I'd likely end up being the poor schmuck who got whacked in the head with the keyboard.
It funny, some people have the "get themselves killed" instinct, and some don't.
I was in a K-Mart store a few years back, when a woman nearby screamed "Hes got my wallet!" as a kid went running out the door.
I dropped my items on the counter (I was in line to checkout) and sprinted after him. About halfway across the parking lot the "WTF am I doing?" logic started to kick in.
Luckily, the kid jumped in a waiting car and took off. All I could do was get the license plate #. As I was walking back to the store, the security officer finally caught up.