Card game some nippers are playing to begin with (4)
I believe the answer is:
snap
'card game' is the definition.
(I've seen this before)
'some nippers are playing to begin with' is the wordplay.
'to begin with' says to take the initial letters.
The first letters of 'some nippers are playing' is 'SNAP'.
(Other definitions for snap that I've seen before include "on the spur of the moment" , "Break sharply like dried twig" , "Break like simple card game" , "Photograph - without warning" , "Informal photograph" .)