A royal ball (3)
I believe the answer is:
orb
'a royal ball' is the definition.
(I've seen this in another clue)
'a royal ball' is the wordplay.
I cannot really understand how this works, but
'royal' could be 'r' (abbreviation) and 'r' is located in the answer.
'ball' could be 'o' (O looks like a ball) and 'o' is found in the answer.
A single letter 'b' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for orb that I've seen before include "Jewelled ornament" , "Heavenly body" , "The World" , "Part of royal regalia" , "Poetically eye" .)