Prize collected by boy, absolutely correct (4-2)
I believe the answer is:
spot-on
'absolutely correct' is the definition.
(spot on means exactly right)
'prize collected by boy' is the wordplay.
'prize' becomes 'pot' (as in a jackpot).
'collected by' means one lot of letters goes inside another.
'boy' becomes 'son' (synonyms).
'pot' placed within 'son' is 'SPOT-ON'.
(Other definitions for spot-on that I've seen before include "Informally precise - no post required" , "Informal expression for precisely" , "Absolutely correct - very accurate" , "Informally precise, receiving no post" , "Exact" .)