Outlaw thanks male, an aggressive little sort (6)
I believe the answer is:
bantam
'an aggressive little sort' is the definition.
(I've seen this before)
'outlaw thanks male' is the wordplay.
'outlaw' becomes 'ban' (banning is a kind of outlawing).
'thanks' becomes 'ta' (UK informal version of 'thank you').
'male' becomes 'm' (common abbreviation).
'ban'+'ta'+'m'='BANTAM'
(Other definitions for bantam that I've seen before include "aggressive little sort" , "Dwarf variety of domestic fowl" , "Small breed of chicken" , "Diminutive breed of hen" , "A cock; one small, aggressive" .)