Sports day event (4,4)
I believe the answer is:
sack race
'sports day event' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for sack race that I've seen before include "Novelty competition on school sports day" , "athletics contest" , "Jumping contest" , "'Novelty competition where entrants run with their feet in a bag (4,4)'" , "event - with 10d" .)