Short sailor exercises after game (6)
I believe the answer is:
abrupt
'short' is the definition.
(abrupt can mean short or terse)
'sailor exercises after game' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'exercises' becomes 'PT' (Physical Training).
'after' says to put letters next to each other.
'game' becomes 'RU' (rugby union).
'pt' put after 'ru' is 'rupt'.
'ab'+'rupt'='ABRUPT'
(Other definitions for abrupt that I've seen before include "Curt, sharp" , "brisk" , "Hurried or curt" , "without warning" , "Unexpected - terse" .)