Doctor who’s bad with old x-ray: do ring practice! (6-3)
I believe the answer is:
shadow-box
'do ring practice' is the definition.
(as in practising for boxing in the ring)
'doctor who's bad with old x-ray' is the wordplay.
'doctor' indicates an anagram.
'with' says to put letters next to each other.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'x-ray' becomes 'x' (phonetic alphabet: alpha, bravo, charlie etc.).
'whos'+'bad'='whosbad'
'whosbad' anagrammed gives 'shadowb'.
'shadowb'+'o'+'x'='SHADOW-BOX'
(Other definitions for shadow-box that I've seen before include "Fight without an opponent?" , "Practise fighting an imaginary opponent" .)