What optical variables are used to guide fielders to catch flyballs and how are these variables mapped onto the action system? A variety of strategies have been proposed for how flyball catching is accomplished, typically entailing fielders maintaining some optic variable constancy (e.g. Optical Acceleration Cancellation, Chapman, 1968; Linear Optical Trajectory, McBeath et al., 1995). However, manipulations in experiments on flyball catching are constrained by the physics of projectile motion. In the present study, we avoid this difficulty through the use of virtual reality. Participants ran to catch virtual flyballs in the VENLAB (using a Cybermind HMD in a 12m x 12m room). By using virtual reality, the physics of flyballs were changed in a manner not possible in a physical environment (e.g. by introducing sudden accelerations to the ball trajectory). An interception model of flyball catching, mapping the available optical variables (e.g. velocities and accelerations of angles to the ball) onto actions variables (e.g. heading and velocity of the outfielder) will be presented, and the effect of different sources of noise on the model will be discussed.