“Gutsy” mariner departs with very little, scratching head (9)
I believe the answer is:
abdominal
'gutsy' is the definition.
(relating to the abdomen or guts)
'mariner departs with very little scratching head' is the wordplay.
'mariner' becomes 'AB' (short for able seaman).
'departs' becomes 'd' (common abbreviation e.g. train timetables).
'with' means one lot of letters go next to another.
'very little' becomes 'nominal' (as in a nominal fee).
'scratching head' means to remove the first letter (the word\'s head is removed).
'nominal' with its initial letter taken away is 'ominal'.
'ab'+'d'+'ominal'='ABDOMINAL'
(Other definitions for abdominal that I've seen before include "Stomachic" , "from a corporation?" , "of part of body" , "Like stomachache" , "like tummy muscles" .)