Ruffle EU -- lots must be upset (6)
I believe the answer is:
tousle
'ruffle' is the definition.
(I've seen this before)
'eu lots must be upset' is the wordplay.
'must be upset' is an anagram indicator.
'eu'+'lots'='eulots'
'eulots' with letters rearranged gives 'TOUSLE'.
(Other definitions for tousle that I've seen before include "Ruffle (the hair)" , "Make hair untidy by ruffling" , "Mess around" , "Make someone's hair untidy" , "Solute (anag)" .)