Score, half of which comes back (3)
I believe the answer is:
net
'score half of which comes back' is the definition.
'net' can be an answer for 'score' (I've seen this before). I am not certain of the rest of the definition.
'score half of which' is the wordplay.
'score' becomes 'line' (lining is a kind of scoring).
'half of' means to take half the letters.
'which' becomes 't' (I can't explain this - if you can you should give a lot more credence to this answer).
'line' cut in half is 'ne'.
'ne'+'t'='NET'
Can you help me to learn more?
(Other definitions for net that I've seen before include "Capture" , "It turns in every direction" , "After taxes" , "Final profit when all overheads have been deducted" , "Mesh for the bottom line?" .)