One large officer, half upset, is unsuitable (3-5)
I believe the answer is:
ill-timed
'unsuitable' is the definition.
(thesaurus)
'one large officer half upset' is the wordplay.
'one' becomes 'i' (Roman numeral).
'large officer' becomes 'llt' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'half' becomes 'demi' (prefix as in 'demigod').
'upset' says the letters should be written in reverse.
'demi' in reverse letter order is 'imed'.
'i'+'llt'+'imed'='ILL-TIMED'
'is' acts as a link.
(Other definitions for ill-timed that I've seen before include "Done or occurring at an inconvenient moment" , "Happening at a badly chosen moment" , "Inopportune" , "Badly scheduled" .)