Lure a girl out? That's irregular (9)
I believe the answer is:
guerrilla
'irregular' is the definition.
('guerrilla' can be a synonym of 'irregular')
'lure a girl out?' is the wordplay.
'out?' indicates anagramming the letters (out can mean wrong or inaccurate).
'lure'+'a'+'girl'='lureagirl'
'lureagirl' anagrammed gives 'GUERRILLA'.
'that's' acts as a link.
(Other definitions for guerrilla that I've seen before include "Irregular soldier" , "Partisan" , "Irregular bandit" , "political insurgent" , "freedom fighter?" .)