Defender returning to the side? (4)
I believe the answer is:
back
'defender' is the definition.
(left-backs and right-backs are football defenders)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for back that I've seen before include "Rear; spine" , "part of the body" , "Support; footballer" , "bet" , "ago" .)