There are crossfit routines for rugby, for soccer, for almost any sport. Crossfit is just the 'marketing name'. Take off head the crossfit routines that you know. Say: 'Crossfit' is like saying, do high reps with low weight in the gym, nothing more. There isn't an ancient art in which you have to follow certain steps, anyone can create their own crossfit routine. As we are on a rugby forum, I think it's best to lose weight without losing muscle mass, and that crossfit is very good for that. Just look at the world's best crossfit exponents and see that they have the body type of an RU internacional back, in some cases have even better body.