Boxing comes in weight classes, and is done professionaly and as amateurs, needed for the Olympic Games.
In the form practiced at the Olympic Games, players have special protective 'helmets' for their heads.
Becoming World Champion in the professional circuit requires challenging the reinging champion. It happens that a reinging champion goes years without being challenged.
Well known are the years of Mohammed Ali and - more recently - Mike Tyson, also famous for biting a piece of his opponents ear.