Grunting in tennis is a widespread phenomenon and whether it influences opponents' predictions of ball trajectory-and if so, why-is subject of ongoing debate. Two alternative hypotheses have been proposed to explain why grunting may impede opponents' predictions, referred to as the distraction account (i.e., grunts capture attentional resources necessary for anticipation) and the multisensory integration account (i.e., auditory information from the grunt systematically influences ball trajectory prediction typically assumed to rely on visual information). To put these competing hypotheses to test, in the current study we presented tennis players with a series of temporally occluded video clips of tennis rallies featuring experimentally amplified, attenuated, or muted grunting sounds. Participants were asked to predict the ball landing position. Results indicated that higher grunt intensities yielded judgments of longer ball trajectories whereas radial prediction errors were not affected. These results are clearly at odds with the distraction account of grunting, predicting increased prediction errors after higher intensity grunts. In contrast, our findings provide strong support for the multisensory integration account by demonstrating that grunt intensity systematically influences judgments of ball trajectory.