Although grip training seems simple on the surface, it’s a little more complicated then most people give it credit for. You can’t just grab something hard and think that it trains your grip strength effectively over time. For example, wrist curls and wrist roller exercises are great for the forearms, but they don’t specifically train the muscles used in gripping. The muscles you need to concentrate on are located in the hand and they don’t run across the wrist (from an anatomical perspective).
I have had coaches suggest to me in the past that they just have their athletes squeeze a tennis ball, but here we have three major issues: