Boxing is a combat sport in which two individuals throw punches at each other in a boxing ring for a specified length of time while wearing protective gloves and other protective equipment such as hand wraps and mouthguards. The referee stops the fight when either boxer fails to make weight or decides it's time to stop the contest. Both boxers wear a headguard that protects their skulls from injury. Heavyweight fighters tend to wear more protective headgear than lightweight fighters because heavy blows are often thrown with greater force and speed and thus require heavier protection. Lightweight fighters usually choose not to wear a headguard because they believe they do not need it. However, many head injuries occur during knockouts when the opponent's head strikes the canvas first before being kicked off by their body. Thus, even though a lightweight boxer may not seem like they need a headguard, it can still save them from serious injury if they are hit hard enough to cause their head to snap back. Heavyweight fighters usually wear a helmet designed for football or hockey. These helmets are made of plastic or steel and have several large openings for the wearer's eyes and a small opening for his/her nose. They also often include a face mask to protect the fighter from getting beaten up around the eyes.