Ache before spring field event (4,4)
I believe the answer is:
long jump
'field event' is the definition.
(long jump is a kind of field event)
'ache before spring' is the wordplay.
'ache' becomes 'long' ('long' can be a synonym of 'ache').
'before' is a charade indicator (letters next to each other).
'spring' becomes 'jump' ('jump' can be a synonym of 'spring').
'long'+'jump'='LONG JUMP'
(Other definitions for long jump that I've seen before include "Field event combining speed and agility" , "Athletics event" , "Sand-pit leap" , "Olympic field event in which Greg Rutherford won gold in 2012" .)