South African’s taking on ten fighters (6)
I believe the answer is:
boxers
'fighters' is the definition.
(boxer is a kind of fighter)
'south african's taking on ten' is the wordplay.
'south african's' becomes 'boer's' (Dutch settler in South Africa).
'taking on' means one lot of letters goes inside another.
'ten' becomes 'X' (Roman numeral).
'boers' placed around 'x' is 'BOXERS'.
(Other definitions for boxers that I've seen before include "Men's shorts for pugilists" , "in the ring with shorts" , "Pugs; dogs" , "Dogs or men's loose underpants" , "Dogs; packers" .)