Gruff sailor's game on exercise (6)
I believe the answer is:
abrupt
'gruff' is the definition.
(thesaurus)
'sailor's game on exercise' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'game' becomes 'ru' (rugby union).
'on' means one lot of letters go next to another.
'exercise' becomes 'pt'.
'ab'+'ru'+'pt'='ABRUPT'
(Other definitions for abrupt that I've seen before include "Curt and brief" , "Curt, sharp" , "without warning" , "Curt and short" , "Gruff" .)