Game fighter's end following jab (5)
I believe the answer is:
poker
'game' is the definition.
(poker game is a kind of game)
'fighter's end following jab' is the wordplay.
'end' indicates one should take the final letters.
'following' means one lot of letters go next to another.
'jab' becomes 'poke' ('poke' can be a synonym of 'jab').
The final letter of 'fighter' is 'r'.
'r' after 'poke' is 'POKER'.
(Other definitions for poker that I've seen before include "Epitome of stiffness" , "Fireside implement - card game" , "Fire iron and card game" , "Jabber" , "Rod liable to become heated" .)