To be competitive, to give 100%, we fear, is to cross the line between what we call adaptive competitiveness into maladaptive competitiveness. If you compete really hard, you're somehow thought to be breaking the rules.
To be a good competitor, you need to know how to go hard without crossing any lines. This is what we get through roughhousing. You learn that these aroused emotions don't have to lead up to fighting or walking away with your soul wounded. Roughhousing is not competition itself, but emotionally, it's sort of a precursor to what you'll experience when you compete.