Seizes brussels sprout, ditching lobsters roughly (6)
I believe the answer is:
usurps
'seizes' is the definition.
(I've seen this in another clue)
'brussels sprout ditching lobsters roughly' is the wordplay.
'ditching' is a deletion indicator.
'roughly' is an anagram indicator.
'brussels'+'sprout'='brusselssprout'
'brusselssprout' with 'lobsters' removed is 'usspru'.
'usspru' is an anagram of 'USURPS'.
(Other definitions for usurps that I've seen before include "Encroaches upon" , "takes place" , "Seizes wrongfully or by force" , "Takes position wrongfully or by force" , "Arrogates" .)