Left back that is certain to get time off (7)
I believe the answer is:
leisure
'time off' is the definition.
(I've seen this before)
'left back that is certain' is the wordplay.
'left' becomes 'l' (common abbreviation).
'back' says the letters should be written in reverse.
'that is' becomes 'ie' ('i.e.' can be a synonym of 'that is').
'certain' becomes 'sure' ('sure' can be a synonym of 'certain').
'ie' back-to-front is 'ei'.
'l'+'ei'+'sure'='LEISURE'
'to get' is the link.
(Other definitions for leisure that I've seen before include "Breathing space" , "Rue lies about rest period" , "Free time; relaxation" , "idle hours" , "retirement" .)