Distance, say, a cart must be raised (7)
I believe the answer is:
yardage
'distance' is the definition.
(distance measured in yards)
'say a cart must be raised' is the wordplay.
'say' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'cart' becomes 'dray' (a cart without sides for delivering heavy loads).
'must be raised' is a reversal indicator (in a down clue, letters go up).
'eg'+'a'+'dray'='egadray'
'egadray' in reverse letter order is 'YARDAGE'.
(Other definitions for yardage that I've seen before include "Distance gained (Am. football)" , "Measurement of length" , "Golf or American Football statistic" , "cost of storing" , "Amount of length (imperial)" .)