Going west in glider really was wrong (5)
I believe the answer is:
erred
'was wrong' is the definition.
(I've seen this in another clue)
'going west in glider really' is the wordplay.
'going west' says the letters should be written backwards (letters heading to the west or left).
'in' indicates a hidden word.
'derre' is hidden in the letters of 'glider really'.
'derre' in reverse letter order is 'ERRED'.
(Other definitions for erred that I've seen before include "Committed a sin" , "Went wrong" , "Was mistaken" , "Strayed from the straight and narrow" , "Made mistakes" .)