The phrase basically means to be aware of your surroundings at all times, so you didn’t get clobbered. Melissa Stark could benefit from that phrase. She was doing her job from the sideline when(with her back to the field as a sideline reporter does) a rogue ball hits her in the back of the head. Two good things about this story 1. She’s okay and 2. She’s able to laugh about it. The video is below and remember-Keep Your Head On A Swivel if you ever find yourself on a NFL sideline.