“The boxer agrees to equip himself with a foul-proof guard of his own selection, type to be approved by the Commission, which will obviate the necessity of any claim being made for a low blow during the contest. It is expressly understood that this contest or exhibition is not to be terminated by a low blow, as the protector selected by the boxers, is, in his opinion, sufficient protection to withstand any so-called low-blow which might incapacitate the said boxer.”