I consider pocket water to be big, fast, gnarly water. Picture rocks the size of washing machines scattered willy nilly with heavy flow in, around and over them creating pockets of tub sized pools, back eddies, etc. Something you would not want to fall into.
In all that madness, fish sit in the calm behind the boulders looking for food to roar by with only a split second to decide if they should go for it.
The Brooks Stone was invented for pocket water. Heavily weighted to get down fast and tied in the round to look the same no matter how it tumbled about.