According to director Jack Hill, it wasn't until they were actually shooting that he learned that Sid Haig, who plays Hawk, the racing champion, didn't know how to drive a car.
Grant Willard: I'm trying to find myself a winner. Racing is a tough business. It's strictly the survival of the fittest. It's just like war: You got a winner and a loser and nothing in between. I busted a lot of heads, training my company in the Marines. But when they got into action, they led the whole Division in decorations received - what was left of them.