Feller putting saddle on ass (10)
I believe the answer is:
lumberjack
'feller putting' is the definition.
(I've seen this before)
'saddle on ass' is the wordplay.
'saddle' becomes 'lumber' (I've seen this before).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'ass' becomes 'jack' (jack is a kind of ass).
'lumber'+'jack'='LUMBERJACK'
(Other definitions for lumberjack that I've seen before include "Feller and transporter of timber" , "Worker felling trees and cutting timber" , "Tree feller" , "American feller" , "Feller putting" .)