During sport, the scrotum contracts to protect the testicles from harm, and in fact, retractile testicles have a protective value in contact sports for this reason – professional sumo wrestlers in Japan actually massage their testicles into their inguinal canals deliberately so they do not become injured during wrestling.
Have you ever seen them fight? It’s like a couple of hippos staggering sideways, crab style, before either kicking each other in where the bollocks ought to be or grabbing their opponent by his nappy. If the film was speeded up and had the Benny Hill yakety yak music added, I reckon it could just be the funniest sight in history.