What exactly is a 'guaranteed purse?'

[Russian Crushin]

In boxing, it just money that is ''guaranteed'' by the fighters promoter to make a fight. The money is almost always deposited into the fighters account the day before the fight; so even if lets say a tornado comes and destroys the arena and cancels the fight, the money is still paid. It is promoter to fighter, not network to fighter. Promoter takes a bit of a risk here

[al-Xander]

It's only applicable in PPV cases, not anything else.

It's a way to convince/persuade the fighter into taking the deal. The guaranteed purse is normally not the amount the fighter accepts in a regular non-PPV fight. He wants more. He can make more if the fight sells. If not, then he's to blame for making the fight boring; promoter didn't promote it well, etc. Plus, fighter/s would have incentive in promoting the fight.