Martin Rogers

USA TODAY Sports

It doesn’t take much for a craze in sports to take off and quickly fade away. But it also doesn't take much in boxing and mixed martial arts to tap out, get knocked out or to speak out in the name of making money.

Which is why the latest hot topic, namely a potential bout between Floyd Mayweather and Conor McGregor, has sparked a whole raft of copycats.

The peculiar thing is that Mayweather, the reigning pound-for-pound boxing king when he retired in 2015, and the noisy, electrifying Ultimate Fighting Championship superstar McGregor, have not yet fought. They are not in training to fight each other. A deal has not even been agreed upon.

It could happen, sure, and if it does the enormous sums of money both men would make prevails as the primary, or maybe only reason.

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Even so, boxers and MMA fighters, either of their own volition or acting on the advice of their advisors, have seemingly started trying to make cross-sport spectacles a common occurrence.

Jimi Manuwa, the No.4-ranked light heavyweight in the UFC, wants to fight fellow Brit and former champion boxer David Haye, rather than trying to secure a title shot in his own division – and his own sport.

Canadian boxer Jean Pascal mouthed off at UFC wild-child Nick Diaz, which is strange, given that Diaz – whose brother Nate split a pair of fights with McGregor – hasn’t fought in more than two years and hasn’t won in nearly six.

If you are a casual sports fan you may not have heard of all these names, or indeed any of them. Which makes the whole exercise fruitless, given that major pay-per-view money, the reason for entertaining such ideas, relies on the casual observer dipping into their pocketbook.

The bigger names are at it too. Manny Pacquiao has said he’d fight McGregor. Nate Diaz would take a crack at Mayweather. And so on.

It is a lot of hot air, something both sports are never short of, but these bouts between boxers and mixed martial artists should not happen. Not because they are unfair, as Mayweather-McGregor patently is. It has already been established the fight would be conducted under official boxing rules, in a boxing ring, with boxing gloves. It is absurd to think McGregor could stand a chance, robbed as he would be of his MMA weapons such as kicks and takedowns.

They should not happen because they don’t and won’t prove anything except that boxers are better than anyone else at boxing and MMA fighters better than anyone else at MMA. Usain Bolt and Michael Phelps are eternal titans of the track and pool, yet either could spot the other a third of the race distance and still probably win.

Vitali Klitschko, who along with his brother Wladimir dominated the heavyweight boxing division for a decade, can be found in online footage getting knocked out during a foray into kickboxing.

His conqueror, Britain’s Pele Reid, went on to box with limited success, never getting as much as a sniff of a title shot.

Mayweather vs. McGregor will be a tough enough sell, albeit one made possible by their personalities and natural matching gifts for verbal shtick. Once we have seen it, it will be enough.

A top-level boxer has tried this once before, when Muhammad Ali took on Japanese wrestler Antonio Inoki in 1976, a bout arranged under mixed rules. It turned into a farce. Inoki spent the entire time laying flat on his back aiming kicks at Ali’s legs. The crowd chanted that they wanted their money back and it ended amid vows it would never be repeated.

Mayweather-McGregor can be stomached once, as long as it goes away afterwards, having shown us nothing and caused plenty to part with their money. But let’s not make it a thing or a trend. When it comes to cross-bred boxing vs. MMA battles: pay up once, satisfy your curiosity, accept it for what it is and don’t be duped again.