In a last trip round South Africa, he committed the attack (9)
I believe the answer is:
assailant
'he committed the attack' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'in a last trip round south africa' is the wordplay.
'trip' indicates an anagram.
'round' means one lot of letters goes inside another.
'south africa' becomes 'SA' (abbreviation).
'in'+'a'+'last'='inalast'
'inalast' with letters rearranged gives 'asilant'.
'asilant' enclosing 'sa' is 'ASSAILANT'.
Can you help me to learn more?
(Other definitions for assailant that I've seen before include "Aggressive sort" , "An attacker like mugger" , "Attacking person" , "One attacking another" , "mugger, say" .)