The upper-cut is the second most valuable punch in your arsenal. The first being the jab. It is a punch that is not thrown often enough. And if it is thrown properly, it can finish off your opponent or set up a combination to end the fight. It can be a swift punch or it can be a power punch, depending on how it is thrown.
To execute the upper-cut, drop your punching hand slightly from the on guard position, just a few inches, then shoot it straight up the centerline of your body. Be sure not to let the punch go beyond the top of your head. Whether it lands or misses, you want to be able to bring your hand back to your on guard position as fast as possible. To throw the punch with a bit more force, bend your knees and upper body slightly, then throw your legs and shoulders into the punch. Remember to keep your rear hand on your face for protection. I can't stress this enough. When throwing an upper-cut to your opponent's body, be sure to bend with your knees slightly. Do not lean forward at the waist! You don't want to lean into your opponent. You will expose your head and make it difficult for yourself to retreat if your opponent tries to counter. Does it seem like I often repeat myself? GOOD! I want to drill this into your head. Keep your hands up. When one hand is punching, the other should be protecting your face, your chin.