Where centre-back is unlikely to be flying (2,3,4)
I believe the answer is:
on the wing
'be flying' is the definition.
(I've seen this before)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for on the wing that I've seen before include "Like birds, often" , "down the touchline" , "(Of birds) flying" , "flier" , "Where one used to see 7 or 11" .)