Express a convinced belief in radical sit-ins (6)
I believe the answer is:
insist
'express a convinced belief' is the definition.
'insist' can be an answer for 'express' (thesaurus). I am not certain of the 'a convinced belief' bit.
'radical sit-ins' is the wordplay.
'radical' is an anagram indicator.
'sit'+'ins'='sitins'
'sitins' is an anagram of 'INSIST'.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for insist that I've seen before include "Be adamant" , "Take no refusal" , "Refuse to give way" , "Be firm in demands" , "Urge" .)