MAIZE BAG / SLIP BAG
The Tear Drop Maize Ball is shaped like a speed bag, except rather than being swelled by an air bladder, the maize bag is filled with first quality textile clippings. It is suspended to the ceiling with a chain, and its weight allows it to swing back and forth quickly. The maize bag is also called the slip bag.
The maize bag is used to practice defense, specifically using head movement (i.e. slipping and ducking) to avoid punches. The maize ball is not meant to be hit. You push it so that it swings back and forth.
Monster Rings and Cages manufactures and sells these bags and they come complete with heavy welded chain and swivel.