It called a "Fight Ball Reflex"
https://www.amazon.com/Reflex-Exercise- ... B01GE12YWU
If you're crafty, you can make them with special tools, or you can buy them online... You need a bunch of them because they wear out very, very quickly compared to a speed bag, heavy bag, double-end bag, skip-rope, bag gloves, sparring gloves, headgear, protector, gum shield, or any other equipment... Even Le Roy hand wraps last longer and don't need replacing as often...