This is a custom at the Westminster School in London, which takes place on Shrove Tuesday (Pancake Day). The earliest references to it date from the mid-eighteenth century. Modern participants often wear fancy dress.
The school cook makes a giant pancake, apparently reinforced with horse hair, which he takes to the dining hall and tosses over the iron bar that runs across the room about twenty feet up. Pupils from each from in the school try to grab a piece. Whoever takes the biggest piece gets a guinea from the Dean. In past centuries, any cook who failed to get the pancake over the bar would be "stoned" with Latin primers.