A ball girl? (7)
I believe the answer is:
crystal
This clue could be a double definition.
'a ball' is the first definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'girl?' is the second definition.
Can you help me to learn more?
(Other definitions for crystal that I've seen before include "Quartz glass" , "brilliant stuff" , "The fortune teller may use a . . . . . . . ball" , "Clear mineral, eg, quartz" , "Cut-glass" .)