Capsized sailor, caught in school, improvised (7)
I believe the answer is:
scratch
'improvised' is the definition.
(I've seen this before)
'capsized sailor caught in school' is the wordplay.
'capsized' says the letters should be written backwards.
'sailor' becomes 'tar' (slang term for a sailor).
'caught' becomes 'c' (cricket abbreviation).
'in' indicates putting letters inside.
'school' becomes 'sch'.
'tar'+'c'='tarc'
'tarc' in reverse letter order is 'crat'.
'crat' put within 'sch' is 'SCRATCH'.
(Other definitions for scratch that I've seen before include "Withdraw from (competition)" , "handle superficial irritation" , "withdraw from event" , "Pull out of match" , "Write hurriedly" .)