I just broke my arm and i am good at rugby i have been ruled out for the season is the anyway i can stat fit a?

I disagree, I'm a forward as well. The worst possible thing that you could do is weight lifting with a broken arm... do you want to make your injury permanent, seriously? Forwards and Backs both need a lot of fitness in long-term and short-term running (sprints). If you feel that you can run without your cast putting too much pressure on your arm then go for it. I don't recommend sprints because they pressure your entire body, and will also pressure your arm, thereby causing damage. Go easy, just remain in shape, when you get your cast off then start lifting weights.