Horseman catching a bandit (6)
I believe the answer is:
raider
'bandit' is the definition.
(thesaurus)
'horseman catching a' is the wordplay.
'horseman' becomes 'rider' (I've seen this before).
'catching' indicates putting letters inside.
'rider' enclosing 'a' is 'RAIDER'.
(Other definitions for raider that I've seen before include "One attacks" , "One who makes a sudden swift attack" , "Depredator" , "Pillager, plunderer" , "person taking food from larder" .)