Mischief-maker’s son finally running in S African event (10)
I believe the answer is:
scapegrace
'mischief-maker's' is the definition.
(thesaurus)
'son finally running in s african event' is the wordplay.
I cannot quite see how this works, but
'son' could be 's' (genealogical abbreviation for son) and 's' is found within the answer.
'event' could be 'race' (race is a kind of event) and 'race' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for scapegrace that I've seen before include "Wayward type" , "Incorrigible (young) rascal - a scarce peg (anag)" .)