I wonder if there are any existing Roman fighting manuals? I haven’t heard of any. I would expect, though, just by virtue of it’s size, shape, and the limitations of body mechanics, that fighting with the gladius would have been similar to (or at least an earlier expression of) the later medieval “I.33” or the “Walpurgis” manual, which dealt with the single-hand shortsword and a buckler.
The Romans were big on role playing as a way to spice up the action. ie: a Retairus (Trident&net) versus the heavily protected Murmillo. The armor was not so much to protect as to prolong the fight. Fights to the death between skilled gladiators was not as common as Hollywood would make you believe. A gladiator was an expensive trained commodity that was not be squandered casually.
The Romans did use criminals, POW’s and various assorted slaves for blood matches. Some Roman citizens even entered training voluntarily. A skilled gladiator was like a rock star of his time.
There were women gladiators altho they were not that common. One of the most famous was Gerardesca Manutius a survivor of the 3rd Servile revolt( Spartacus). She was spared crucifixion by Crassus and sent to the arena. She had over 200 victories over both men and other women gladiators before dying in a match against 2 dwarfs.