Isn't it only because of there stocky builds and high muscle mass that they are classed as such because it makes them so heavy, not because of excessive body fat?

Rugby players are strong not fat.. if you go off BMIs etc then a short very muscular player may some how manage to fall into the obese category but these men are not unhealthy, their training and nutritional diets are for being physically capable to play their game.. Their mass comes from muscle not fat.