To annoy deer, cut grass back (6)
I believe the answer is:
rankle
'to annoy' is the definition.
(rankling is a kind of annoying)
'deer cut grass back' is the wordplay.
'deer' becomes 'elk' (type of deer).
'cut' means to remove the last letter.
'grass' becomes 'knar' (I can't explain this - if you can you should believe this answer much more).
'back' shows that the letters should be reversed in order.
'elk' with its final letter taken off is 'el'.
'el'+'knar'='elknar'
'elknar' backwards is 'RANKLE'.
Can you help me to learn more?
(Other definitions for rankle that I've seen before include "Cause continuing irritation" , "Continue vexing" , "Embitter" , "Cause continuing annoyance or resentment" , "Fester" .)