Adding to the point that Jarrod, Omar and myself had reiterated, another "price" I think is very important to mention is the bumps and bruises we've all taken at one time or another. Now there may be a fine line between an injury that requires medical attention, and one that doesn't. When it does require medical attention, guess who's going to pay that bill? And if it's something as minor as a bruise or bloody nose, running to the parents will probably result in "I told you so" and possibly a hiatus in one's training.