Book 28, Question 28
Why do baseball pitchers use a rosin bag?
The rosin bag is a small cloth bag filled with powder made from pine tree sap.
Pitchers pat it to dry sweat on their hands and give them a bit of tackiness, so the ball doesn't slip. Rosin helps pitchers keep a steady grip even on hot days. Musicians who play violins and cellos rub the same stuff on their bow hair.