what are the differences in terms of mechanics?? How are both properly thrown?
The cross is a straight right hand. You are sinking your hips, turning your hips and body and driving the power up from the floor through your body and into the opponent's head. It's a powerhouse punch and a lot of people's bread and butter. Best set up with a double jab, jab and fake or as a counter to one of your opponent's straight punches.
The overhand is rather unorthodox. It's very effective if thrown, timed and connected properly but those three factors have to be perfect or you will find yourself off balance and wide open to be taken down or counterpunched by a skilled opponent.
The overhand right is best thrown as a secondary or tertiary punch into a simple combination. Never try to lead with it. The only time I would try to counter with it is if I were fighting a southpaw and stepping/dipping away from his jab (I am an orthodox boxer) and he was less skilled than I. Best done just after the opponent finalizes a combination and you slip or successfully parry/defend against his combo. Best followed up by a hook (most people think an uppercut is the best follow-up, but the weight shift on a proper overhand right is pretty dramatic, setting you up perfectly to throw a hook)
DON'T make the mistake of thinking that an overhand right has the same body mechanics as a cross with a looping trajectory. It absolutely does not. I'll walk you through the mechanics:
Your combination will be: Jab-Cross-Hook-Overhand Right-Hook from an orthodox stance (left hand/left foot forward). This will get you 'in tune' with the proper body mechanics. Now, jab, then when you cross you want to turn your hips all the way over and turn your shoulder all the way. All of your weight should be on your FRONT foot. I should be able to kick your back leg out from under you without you falling. Now, when you hook, step to the right side with all of your weight onto your RIGHT LEG. Your hips should be turned all the way to the right, and your right hand should be like you are on the phone. Now when you throw the overhand right you are going to transfer all of your weight back onto your left foot but instead of stepping your left foot forward you will step it to the left side. Twist your body to the left so your right shoulder is reaching toward the target when you throw it. When you complete this punch your chin should be in your right shoulder, and your left hand should be like you are on the phone. When you throw the last hook transfer weight back to your right leg.
The motions sound more dramatic in a written description than they actually are. Anyway, if you are training in MMA or are new to boxing I would stick with the cross for a long time until you can land it at will. It's got dynamite stopping power and sets up the hook beautifully. Any other questions, please let me know.
Great thanks to all!