Find it impossible to turn about at a fast pace (6)

I believe the answer is:

canter

I'm a little stuck... Click here to teach me more about this clue!

'pace' is the definition.
(I know this)

I don't understand how the rest of the clue works.

(Other definitions for canter that I've seen before include "Move at an easy gallop" , "Trance (anag) - horse's pace" , "Moderate pace for horse" , "Pace of a horse between trot and gallop" , "Ride at a quick pace" .)

I've seen this clue in the Evening Standard.

Want a hint initially instead of a full solution? Install my app