Boxing is divided into weight classes to accommodate fighters of all different shapes and sizes while maintaining sporting integrity.
Athletes, such as the unified WBA, IBF, and WBO heavyweight champion Oleksandr Usyk, have to manually move up in weight through dieting and gym work to compete across boxing's 17 different weight divisions.
The Ukrainian was a former undisputed cruiserweight king before he began to emulate Evander Holyfield and David Haye in challenging heavyweights.
But in certain cases it's in both fighters interests to agree to fight outside of an existing weight division...
A catchweight describes an agreed weight limit that is outside the traditional limits of a boxing weight class.
This could be because the two opposing rivals don't want to either cut or bulk up a full weight class from what they typically compete in and risk effecting performance.
The most notable example in recent times was Kell Brook's win over Amir Khan in which the pair agreed to fight at 149lbs - two pounds above the standard welterweight limit.
Notable rivals Conor Benn and Chris Eubank Jr's on-off grudge showdown would also need to take place at a catchweight.
Eubank Jr has spent his career campaigning at middleweight (160lbs) and super-middleweight (168lbs).
But he agreed to weigh 157lbs in order to meet Benn – who is typically a welterweight (147lbs) – at a catchweight.
Usually catchweight fights come with the stipulation that any fighter that fails to then meet the agreed-upon weight would face a purse penalty.
They would also feature rehydration clauses that limit how much a boxer can put back on after the weigh-in and prevent weight mismatches that can endanger the 'smaller' fighter.
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