Judge of performance regularly displayed acerbic twitch (6)
I believe the answer is:
critic
'judge of performance' is the definition.
'critic' can be an answer for 'judge' (critic is a kind of judge). I'm unsure of the 'of performance' bit.
'regularly displayed acerbic twitch' is the wordplay.
'regularly displayed' means one should take alternating letters (letters selected on a regular basis).
'twitch' becomes 'tic' (tic is a kind of twitch).
The alternating letters of 'acerbic' are 'cri'.
'cri'+'tic'='CRITIC'
Can you help me to learn more?
(Other definitions for critic that I've seen before include "(Eg, theatre) reviewer" , "Arts reviewer" , "Writer of reviews" , "Judge of literary or artistic works" , "Reviewer of book or play" .)