Truthfully, if you play outfield. Go to a showcase that has outfield. If you go to a showcase unprepared (especially at SS then it's not good because of the high chances that you will not preform at a good level.) You should probally just wait to go to showcase that includes outfield. Why would you try out infront of scouts when your not even playing your TRUE position? And the answer to you question is they grade you on both position ability and overall(SS having, strong arm, quick feet and release, speed, and clean fielding.)