Combat a charge to support king (6)
I believe the answer is:
karate
'combat' is the definition.
(I've seen this before)
'a charge to support king' is the wordplay.
'charge' becomes 'rate' (rate is a kind of charge**).
'to support' means one lot of letters go next to another (in a down clue, some letters hold others up).
'king' becomes 'k'.
'a'+'rate'='arate'
'arate' after 'k' is 'KARATE'.
(Other definitions for karate that I've seen before include "method of fighting" , "A taker (anag)" , "Japanese art of unarmed combat" , "SPORT/GAME" , "Martial art (with chopping?)" .)