Stumble before the French start event (6,4)
I believe the answer is:
triple jump
'event' is the definition.
(I've seen this before)
'stumble before the french start' is the wordplay.
'stumble' becomes 'trip' (synonyms).
'before' is a charade indicator (letters next to each other).
'the french' becomes 'le' ('the' in French).
'start' becomes 'jump' (synonyms).
'trip'+'le'+'jump'='TRIPLE JUMP'
(Other definitions for triple jump that I've seen before include "Athletic event" , "Three-step event" , "Athletics event" .)