Swimmer's hair getting cut back on top (7)
I believe the answer is:
pollock
'swimmer's' is the definition.
(type of fish)
'hair getting cut back on top' is the wordplay.
'hair' becomes 'lock' (a lock of hair).
'getting cut back' becomes 'pol' (I am not sure about this - if you are sure you should believe this answer much more).
'on top' means one lot of letters go next to another (in a down clue, some letters go above others).
'lock' after 'pol' is 'POLLOCK'.
Can you help me to learn more?
(Other definitions for pollock that I've seen before include "Artist" , "See 9" , "Fish" .)