In a football game when an offensive player blocks a defensive player, knocks him off his feet and causes him to fall flat on his back. The offensive player may lay on top of the defensive player to add insult to injury.
"I can't believe Sally is getting clapped from back, oh wait when did Johnny get here? Oh no he turned her around and he's hitting it from the front she's getting flipped like a Pancake!!!!" Pancaked
Typically used as a football term meaning to "lay a kid out" or to deck someone". Being pancaked is embarrassing if you are the one being pancaked. On the flip side, pancaking someone is a feat of strength and a play no one will forget.