Ban learner stuck in reverse (5)
I believe the answer is:
black
'ban' is the definition.
(I've seen this in other clues)
'learner stuck in reverse' is the wordplay.
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'stuck in' is an insertion indicator.
'reverse' becomes 'back' (I've seen this before).
'l' put into 'back' is 'BLACK'.
(Other definitions for black that I've seen before include "Can precede art, box, eye" , "Extremely dark" , "Gloomy" , "Served without milk" , "Uncommon H [HORSE]" .)