The Latin anglicism for ultimate guts and bravado. Following from Balls of Brass (
British), Balls of Steel (Duke Nukem), Balls of Titanium (Iron
Man), Balls of Adamantium (Wolverine), Balls of Unobtonium, etc, etc, a new term was needed to most specifically describe the new level of racing prowess displayed in WSBK and MotoGP racing. The term can be used in any other context where skills, ability and guts/bravado is of super-human/
hero caliber.