Breathe hard, needing oxygen for stage show (5)
I believe the answer is:
panto
'stage show' is the definition.
(I know that panto is a type of stage show)
'breathe hard needing oxygen' is the wordplay.
'breathe hard' becomes 'pant' (I've seen this before).
'needing' says to put letters next to each other.
'oxygen' becomes 'O' (O is the chemical symbol for oxygen).
'pant'+'o'='PANTO'
'for' acts as a link.
(Other definitions for panto that I've seen before include "Christmas entertainment (abbr.)" , "Trad. Christmas fun (abbr.)" , "In brief, traditional Christmas entertainment" , "Fun for kids" , "Cinderella or Puss in Boots, say?" .)