A pain in the neck starts to explain the game (7)
I believe the answer is:
cricket
'game' is the definition.
(I know that cricket is a type of outdoor game)
'a pain in the neck starts to explain the' is the wordplay.
'a pain in the neck' becomes 'crick' (I've seen this in another clue).
'starts to' suggests taking the first letters.
The initial letters of 'explain the' is 'et'.
'crick'+'et'='CRICKET'
(Other definitions for cricket that I've seen before include "Jumping insect" , "short leg seen on this field?" , "English game or chirping insect" , "Game - "basically baseball on Valium" (Robin Williams)" , "a jumper" .)