Avoid setter perhaps penning last bit of crossword with ecstasy (5)
I believe the answer is:
dodge
'avoid' is the definition.
(I know that avoid can be written as dodge)
'setter perhaps penning last bit of crossword with ecstasy' is the wordplay.
'setter perhaps' becomes 'dog' (setter is a type of dog).
'penning' means one lot of letters goes inside another.
'last bit of' says to take the final letters.
'with' is a charade indicator (letters next to each other).
'ecstasy' becomes 'E' (informal term for the drug).
The last letter of 'crossword' is 'd'.
'dog' going around 'd' is 'dodg'.
'dodg'+'e'='DODGE'
(Other definitions for dodge that I've seen before include "Avoid by a quick move" , "Cunning move" , "Get out of" , "Take evasive action" , "Move quickly to avoid" .)