Some hero under six in game (8)
I believe the answer is:
rounders
'game' is the definition.
(rounders is a kind of game)
'some hero under six' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'ROUNDERS' is hidden within 'hero under six'.
'in' acts as a link.
(Other definitions for rounders that I've seen before include "Baseball for kids?" , "Game like baseball" , "Game similar to baseball" , "Bat-and-ball game" , "Local form of American baseball" .)