Exclamation made by clumsy sailor about work? (4)
I believe the answer is:
oops
'exclamation made by clumsy' is the definition.
'sailor about work?' is the wordplay.
'sailor' becomes 'os' (ordinary seaman).
'about' means one lot of letters goes inside another.
'work?' becomes 'op' (abbreviation for opus**).
'os' enclosing 'op' is 'OOPS'.
(Other definitions for oops that I've seen before include "Harem" , "Exclamation on making minor error" , "Exclamation of surprise or apology when making mistake" , "Apologetic exclamation" , "My bad" .)