Attack tree-hugging oaf (4,3)
I believe the answer is:
lash out
'attack' is the definition.
(I've seen this before)
'tree-hugging oaf' is the wordplay.
'tree' becomes 'ash' (ash is a kind of tree).
'hugging' means one lot of letters goes inside another (inserted letters are hugged).
'oaf' becomes 'lout' (synonyms).
'ash' put into 'lout' is 'LASH OUT'.
(Other definitions for lash out that I've seen before include "Spend extravagantly" , "fight vigorously" , "Strike (or spend) wildly" , "Become suddenly aggressive" , "unprovoked attack" .)