Jeremy I am assuming that you just want to give away 10 points rather than search this exact same question. It marks the person wearing to wireless mic in his helmet. This question is asked at least 5 times a day for the last 3 weeks.

It is to signal to referee which player is wired (QB's communication system)

I guess a team had 2 QBs on field at same time last year and both had wireless system. Somhow NFL thought it should change the rule

Heard Madden talk about it during Giants/Ravens preseason game

Green dot on a helmet means that the helmet is equipped with a radio device for communication with the coach. No two helmets with the green dot can be on the field at the same time. Backup QBs sometimes holds the ball during a field goal. Last year a fake field goal was called during a game with the backup QB holding and he had the helmet with the communication device. Now, opposing teams andd refs can identify who is communicating with the coach.

It is a cool new feature of Madden 08 which lets you control the QB from home with you Xbox 360 controller. I like to be Tom Brady....I make him fall down a lot.

I love Madden!