This study determines the effects of three baseballs and softballs of different masses (0.113 kg, 0.198 kg, 0.340 kg) and regulation diameters (22.86 and 30.48 cm, respectively) on the glenohumeral horizontal abduction angle of an overarm throw performed by young children who were novice throwers. Glenohumeral horizontal abduction angle was operationally defined as a relative angle greater than 180[degree] between the humerus and the trunk (determined by a line from the lateral epicondyle to the acromion and the line between the acromions). Based on past research using adult throwers, it was hypothesized that the glenohumeral horizontal abduction angle would differ with the balls of various sizes and masses. Specifically, it was hypothesized that the increased mass of the ball would increase the mass (inertia) of the hand, making the hand-ball system more resistant to a change in its motion, from the drawing back of the arm, to the ballistic movement forward. Theoretically, a more massive hand would force the more proximal segments to proceed posteriorly during the cocking phase of the throw. This increased posterior movement would result in an increased angle between the trunk and upper arm, indicating a greater glenohumeral horizontal abduction angle. In addition, it was speculated that the increased size of the ball would produce less glenohumeral horizontal abduction angle, because the participants would move the object closer to the midline and adopt a more pushlike (simultaneous) motion. The novice throwers in the study failed to achieve demonstrable change in the glenohumeral horizontal abduction angle, which may be attributed to the relatively small angle between the trunk and the upper arm produced by novice throwers. This is consistent with the implication that there will be more of a pushlike simultaneous motion in these throwers, rather than the sequential whiplike motion typically demonstrated with a temporal and spatial lag in the forward movement of the humerus. In addition, the dramatic variability of the performance of the novice throwers, demonstrated by the high standard deviations of the relative glenohumeral horizontal abduction angle, further indicates that a consistent throwing pattern had not yet been achieved by the participants. This may have been the result of inconsistencies in ball size, grip size, grip strength, and/or the restriction of degrees of freedom of the participant in an attempt to perform an overarm throw under new task constraints. (Contains 3 figures.)