I hate people who only play one or two mainstream games then call them selves gamers... Like I know TECHNICALLY they are gamers, because they play games, but if all you do is play CoD or Halo, or what ever big name group, I do not consider you a gamer, I just call you a talented casual gamer if you're good at it, or if you are not just a casual gamer.
You become a gamer in my mind, when you know about other games that don't have 24/7 adverts on TV, and read up on gaming related news. For the most part everyone on this forum I would consider a gamer, regardless t oskill as you most likely read the articles upon gaming. +1 to you chaps.
Wait, this is kinda off topic...
Oh and to answer one, nerd is associated with a pasty fat white kid in a basement playing D&D, where as A footballer is associated with a tan muscled dude, that has tons of girls hanging around him. It's just the image that comes along with the name that has the "Sting" to it, remove the image from nerd, and it'll become the near same thing to Football, not a insult just a title.