Leaderless emu fit to change into civilian clothes? (5)
'civilian clothes?' is the definition.
(I've seen this before)
'leaderless emu fit to change' is the wordplay.
'leaderless' means to remove the first letter.
'to change' indicates anagramming the letters.
'emu' with its initial letter taken off is 'mu'.
'fit' is an anagram of 'fti'.
'into' is the link.
(Other definitions for mufti that I've seen before include "Civilian dress, in army terms", "Civvy dress", "Plain clothes - Muslim law expert", "For soldiers, civilian dress", "Civilian clothing for a military person".)