As gets posted regularly, my advice would be that you either go to a game to watch it OR you go to photograph it. Not both.
Go watch the game, leave the camera at home, you'd probably get fairly crap photos from the stands and it is against regulations. If you want to photograph rugby, go about it the right way. Get in touch with a club, talk to some one, don't just turn up and start taking photos (I'm not suggesting you would). In my experience you'll find that there will be a club that will have no problem with you photographing, normally they will expect a couple of images in return though.
Again, my advice, don't give everything over for free. If you are totally up front about what you're doing you tend to get more positive reaction.
Also, (not saying it's you again!) I don't get a lot of people's obsession with trying to photograph the absolute highest level possible from day 1. Sure, having big crowds as a back drop to your best action shots is better than a car park, and the atmosphere is great, but to hone your actual shooting skills at a level with easy access is more important in my opinion. Don't dismiss your local smaller clubs, they'll be more likely to let you photograph and the players and their families may actually be more likely to ask to buy a print off you! Just because it's not professional doesn't mean it doesn't make good images.
On the other point, personally I'd never shoot a game if I had to pay to do it, the whole point is trying to do it the other way round!