Counter assists checking at match venues (6)
I believe the answer is:
stadia
'match venues' is the definition.
'stadia' can be an answer for 'venues' (I have seen 'major venues' mean 'stadia' so perhaps 'venues' could also mean 'stadia'). I'm not sure about the 'match' bit.
'counter assists checking at' is the wordplay.
'counter' is a reversal indicator.
'assists' becomes 'aids' ('aid' can be a synonym of 'assist').
'checking' is an insertion indicator (check can mean to control or arrest).
'aids' placed around 'at' is 'aidats'.
'aidats' back-to-front is 'STADIA'.
Can you help me to learn more?
(Other definitions for stadia that I've seen before include "Sports arenas" , "Large sports venues" , "major venues" , "Athletics grounds" , "large arenas" .)