Rosin powder eliminates grip problems resulting from humid air or sweat. Small rosin bags are inexpensive, fit in small sports-bag pockets and can be found in the baseball section of sporting goods stores. Take the bag and lightly toss it in the air with the sweaty hand. Catch it and toss it again. Repeat until a desired amount of powder puffs onto your palm and fingers. Use the opposite hand to lightly tap the bag onto the back of your sweaty hand, wrist and forearm, to prevent sweat from dripping down the arm. Practice your sport with rosin to get a feel for the appropriate amount; too much powder may clump with sweat. Rosin can help you grip anything, such as a baseball bat, a golf club, a bowling ball or a tennis racket.