OK, so you see a guy with a knife running around chasing someone just like out of a horror movie, what do you do? Well, if you listen to the police (that’s a link, Glenn ), you would do nothing:

A knife-wielding grocery store employee attacked eight co-workers Friday, seriously injuring four before a witness pulled a gun and stopped him, police said.A knife-wielding grocery store employee attacked eight co-workers Friday, seriously injuring four before a witness pulled a gun and stopped him, police said.
[…]
Ingram, chasing one victim into the store’s parking lot, was subdued by Chris Cope, manager of a financial services office in the same small shopping center, Memphis Police Sgt. Vince Higgins said.
Cope said he grabbed a 9mm semiautomatic pistol from his pickup truck when he saw the attacker chasing the victim “like something in a serial killer movie.”
“When he turned around and saw my pistol, he threw the knife away, put his hands up and got on the ground,” Cope told The Associated Press. “He saw my gun and that was pretty much it.”
[…]
The spokeswoman said officials from the St. Louis-based company were on their way to the scene.
Higgins said police were pulling into the parking lot as Cope was confronting Ingram.
“We commend him,” Higgins said. “But we don’t encourage people to take that kind of risk. He could have been hurt.“

OK, so what is the lesson learned from this officer? Well, if confronted by a knife-wielding maniac, we should do nothing even though we have a gun. We should do nothing and hope that we don’t get stabbed or that the person that is being chased isn’t stabbed to death before the police get there. Yes, that sounds like a plan.