Capturing a record in the comeback is one's aim (4)
I believe the answer is:
goal
'one's aim' is the definition.
'goal' can be an answer for 'aim' (I've seen this before). I'm not certain of the 'one's' bit.
'capturing a record in the comeback' is the wordplay.
'capturing' indicates putting letters inside.
'record in the comeback' becomes 'gol' (I can't justify this - if you can you should give a lot more credence to this answer).
'a' going inside 'gol' is 'GOAL'.
'is' is the link.
Can you help me to learn more?
(Other definitions for goal that I've seen before include "Object of one's ambition" , "Crossbar, posts and nets" , "Target (best not one's own!)" , "Ambition for a score" , "Object, aim" .)