When someone drops something, and it falls in their lap. It mostly occurs when the person is sitting. When dropping something while standing, the person will catch the item by pushing it against their crotch in a fast motion to stop it from falling.
During Biology, Mia dropped her pencil. She put her hands down to catch it, only to realize that her crotch caught it instead of her pencil falling the the floor.
Steve: "Crotch Catch!"
Mia: "Stfu Steve."