Final part in hand (4,8)
I believe the answer is:
home straight
'final part' is the definition.
I know nothing about this answer so I can't judge whether this works.
'in hand' is the wordplay.
'in' becomes 'home' ('he's in' can mean 'he's home').
'hand' becomes 'straight' (I've seen this before**).
'home'+'straight'='HOME STRAIGHT'
Can you help me to learn more?
(Other definitions for home straight that I've seen before include "Last part of a race" , "final stage of race" , "Final stage of a racecourse" , "Last stage of race" , "covered in neat report" .)