On first look it seems a contradiction, a fat, seemingly out of shape guy beating someone who by comparison looks much much more fitter. But that fat helped.
In certain sports or scenarios, carrying extra body fat is very beneficial. Ancient gladiators and fighters new the benefits of adding body fat – one of which was protecting the body from blows, and cuts. Fat can act as a natural body armour – protecting vital organs.
This is of no use to the general population, nor would it suit someone who was into running or cycling. But to a boxer/ fighter, extra fat will come in very handy.
That extra fat also means that each blow will carry more weight. If your carrying an extra 10kg, even if its fat, your opponent is goign to feel the blow of your punch a whole lot more.
The Cost: Under all the fat you need to be very fit and strong. Andy Ruiz Jr is extremely agile, and has allot of muscle under his fat, his fitness levels will be through the roof, so there is no need for him to ‘tone up’. That is the difference between him and say your average fat person – the average fat person is nowhere near as fit, nor are they carrying anywhere near as much muscle.