What an air ball doesn't touch (3)
I believe the answer is:
rim
'what an air ball doesn't touch' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for rim that I've seen before include "Edge or margin" , "Flange" , "Brink" , "Circumference" , "'Brim, lip (3)'" .)