Pace is lacking in case (6)
I believe the answer is:
canter
'pace' is the definition.
(cantering is a kind of pacing)
'is lacking in case' is the wordplay.
'lacking in' indicates named letters should be taken away.
'case' becomes 'canister' (I've seen this before).
'canister' with 'is' taken out is 'CANTER'.
(Other definitions for canter that I've seen before include "Trance (anag) - horse's pace" , "(Horse's) pace between a trot and a gallop" , "A slow easy gallop as for horse" , "Move at an easy gallop" , "Pace of a horse between trot and gallop" .)