Purist movement in trouble (4,2)
I believe the answer is:
stir up
'trouble' is the definition.
(thesaurus)
'purist movement' is the wordplay.
'movement' indicates an anagram (letters move around).
'purist' anagrammed gives 'STIR UP'.
'in' acts as a link.
(Other definitions for stir up that I've seen before include "Get excited" , "Excite - incite" , "Foment (trouble)" , "Cause or provoke trouble" , "Instigate" .)