The hook grip will stop the barbell from turning while gripped in the hands unlike a conventional grip. A conventional grip of thumb over the fingers can produce more force; however it is not the most secure grip to use. The hook grip is achieved by wrapping the thumb around the bar first and then wrapping the pointer and middle finger around the thumb.There are two ways to unhook the hook grip. The first way is done naturally when a lifter flips their palms up. Other lifters might have to unhook after the squat and then prepare for the jerk. Most lifters will use a conventional grip when jerking the barbell.
Initially the lifter who is first using the hook grip will experience pain in the thumb. This is normal to a person who has never conditioned their hands to the hook grip. Some beginners will also have the thumb bruise (turn black and blue) this is normal and will pass with time. If the lifter experiences too much discomfort from the hook grip they should only do some lifts with the hook grip will using a conventional grip for other exercises. Eventually the lifter will build up a tolerance to the pain while using the hook grip and will be able to use it all the time.The picture below is what the hook grip looks like