Effect of grip-enhancing agents on sliding friction between a fingertip and a baseball

Friction between a pitcher’s fingers and the leather surface of a baseball is a key factor that influences ball delivery, causing Major League Baseball in the United States to recently enhance enforcement of rules banning the unauthorized use of friction-enhancing agents or sticky substances. Here, we examine how the application of rosin powder and sticky substances alters the friction coefficient between a fingertip and the leather of a baseball. We find that sticky substances increase friction which can positively affect ball spin rate, while rosin has the advantage of keeping friction consistent within and between individuals. Additionally, we find that baseballs used by the Nippon Professional Baseball Organization in Japan are less slippery compared with the ones used in Major League Baseball, suggesting that grip-enhancers may have a larger impact on friction for baseballs used in the United States compared to Japan. Furthermore, our results indicate that changing the characteristics of the leather the baseball is made from may increase friction, reducing the unauthorized use of sticky substances.