Seems put out - may become violent (11)
I believe the answer is:
tempestuous
'violent' is the definition.
(thesaurus)
'seems put out may become' is the wordplay.
'may become' indicates anagramming the letters.
'seems'+'put'+'out'='seemsputout'
'seemsputout' is an anagram of 'TEMPESTUOUS'.
(Other definitions for tempestuous that I've seen before include "Very stormy" , "Seems put out (anag)" .)