Irregular and liberal — mostly irregular and liberal (9)
I believe the answer is:
guerrilla
'irregular' is the definition.
(I know that irregular can be written as guerrilla)
'liberal mostly irregular and liberal' is the wordplay.
'liberal' indicates an anagram.
'mostly' means to remove the last letter.
'and' says to put letters next to each other.
'liberal' becomes 'l' (abbreviation).
'irregular' with its final letter taken away is 'irregula'.
'irregula' put after 'l' is 'lirregula'.
'lirregula' anagrammed gives 'GUERRILLA'.
'and' acts as a link.
(Other definitions for guerrilla that I've seen before include "Member of politically-motivated fighting group" , "Member of an irregular armed force" , "in conflict to secure political end?" , "Irregular bandit" , "Person who fights as one of small independent group" .)