Aerodynamics of vertical slider changing baseball ball is studied by wind tunnel experiment data. The direction of the good vertical ball rotation axis orients toward the home base, straightly. And sharp drop trajectory is observed with less lift force. In the case of slightly change of orientation of rotation direction of spinning axis, how about aerodynamic characteristics and resultant trajectory is? According these small change of the rotation direction angle ranging +10°〜+30°, strange aerodynamic forces appeared on ball air force. These results well explain the real direction shift of ball spinning axis and the resulting ball trajectory of Meager League pitcher named D. Matsuzaka.
