Definitions of middleweight:

• noun:   a professional boxer who weighs between 155 and 160 pounds
• noun:   a wrestler who weighs 172-192 pounds
• noun:   an amateur boxer who weighs no more than 165 pounds
• adjective:   of middle weight or of a middleweight category (155-160 lbs for prizefighters)

  Example: "A middleweight boxer"