What kind of sensor could detect the valve of a rotating soccer/rugby ball?
This is probably best done using machine vision.  Have a camera look at a section of the ball at this "home position".  Rotate the ball in a pattern so that every part of the ball is exposed to the camera each time thru the pattern.  At regular intervals, the picture is examined by software, and a attempt is made to find the valve.  If the valve is not seen, continue the pattern.  If the valve is seen, then stop the pattern and move the ball to position the valve as desired.