Spectators need to show electronic approval (4)
I believe the answer is:
eyes
'spectators need' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'electronic approval' is the wordplay.
'electronic' becomes 'e' (as in e-mail or e-books).
'approval' becomes 'yes' (I've seen this in another clue).
'e'+'yes'='EYES'
'to show' acts as a link.
Can you help me to learn more?
(Other definitions for eyes that I've seen before include "Scans" , "They see and" , "Visual organs" , "Potato seed-buds" , "Needle holes" .)