Strikes vessel without banging in it (3,3)
I believe the answer is:
sit ins
'strikes' is the definition.
(type of industrial action or strike)
'vessel without banging in it' is the wordplay.
'vessel' becomes 'ss'.
'without' means one lot of letters goes inside another ('without' can be similar in meaning to 'outside').
'banging' indicates anagramming the letters (the order of letters is banged up or smashed).
'in'+'it'='init'
'init' anagrammed gives 'itin'.
'ss' going around 'itin' is 'SIT-INS'.
(Other definitions for sit ins that I've seen before include "demonstrations" , "Signs of protest" .)