Wheel leveling affects ball trajectory by altering the angle at which the ball is released from the cue. When the cue is leveled properly, it promotes a more consistent and accurate shot, resulting in a predictable trajectory. An improperly leveled cue can lead to unintended spin or elevation changes in the ball's path, affecting both distance and direction. This adjustment in the cue's angle can influence how the ball interacts with the table's surface and other balls, ultimately impacting the overall outcome of the shot.