Gladiator footwear

[Martin Moser]

the ground we fight on is not smoothly raked sand. It may contain broken bottles, grass burrs, sharp sticks, etc., which do considerably to distract us when we are having our exhibitions.

Sounds like an acceptable reason :-) )

We know that it's not authentic, but neither is fighting with non-lethal weapons

That actually is authentic, it was done in the prolusio apparently. Skipping the following round is what's not authentic ;-) )