The best way to determine if a bunt should be called on the attempt is if moves the bat toward the ball. You will be told the proper method for bunting is to "catch the ball with the bat" so you actually move it backwards from the ball. Even using that you still have to move the bat toward or in the path of ball. If he squares and does nothing else then call the pitch on location. If the batter does anything you deem as go after the ball the you have an attempt. Hope this helps.