In the first Battle scene in the Coliseum. One of the Gladiators calls Crowe Maximus before tossing him a sword. This is prior to him revealing his name to the Emperor and the others.
Well, it's the black dude that he is friends with that says his name. Maybe he told him what his name was. Or maybe he goes to Cheers and knows everybody's name.
Well in the movie the colluseum was very big, and there was two parts to the colluseum the audience area and the area where Maximus was so when the guy shouted his name it was hard to hear from where the emperor was it was high. when he looked at the people fighting all he could do is see the fighting but he can't hear because of the the height and the crowd and the greatness of the arena.
OK, about the name... When Maximus is talking about how they can stay alive by sticking together, one of the other gladiators says I fought with you at blah blah blah... anyway, at this point someone knows his name and maybe thats how they knew it...
Travis
Well if you remember when Russell (Maximus) says "Anyone here ever been in the army?" (or something similar) someone says "I served with you at Vindabona." So, you can sort of conclude that perhaps he knew his name and told everyone else. Just a hypothesis. However, I don't remember anyone telling Maximus Hagen's name because after Hagen gets hit in the leg with the arrow, Maximus yells "Hagen!" and runs to save him. So, that part could be a slipup.. or not...