Game Carol plays with sister regularly (8)
I believe the answer is:
lacrosse
'game' is the definition.
(lacrosse is a kind of game)
'carol plays with sister regularly' is the wordplay.
'plays with' is an anagram indicator.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternate letters of 'sister' are 'sse'.
'carol' mixed up with 'sse' can make 'LACROSSE'.
(Other definitions for lacrosse that I've seen before include "Ball game using netted stick" , "Score's uncertain after the Spanish" , "Game played with a netted stick" , "Sport played with sticks" , "Like thirteen of the other clues in the French" .)