A method for calculating a repeatability index of gestures and shots of a player striking a tennis ball with a racket having attached measurement sensors. The method includes conducting an initial series of shots to measure vibration, angular velocity, and linear acceleration of the racket during each shot to generate behavioral data of the racket corresponding to each shot of the initial series, and later comparing the measured vibration, angular velocity and linear acceleration of the racket to shots of a further series to determine the type of hit and a repeatability index indicating an ability of the player to identically repeat each of the type of hit.