'Let's hear it for the ordinary potato' -- one expressing opinion (11)
I believe the answer is:
commentator
'one expressing opinion' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'let's hear it for the ordinary potato' is the wordplay.
I cannot quite see how this works, but
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is found in the answer.
'for' could be 'to' (eg both can mean 'in the opinion of') and 'to' is found in the answer.
'ordinary' could be 'o' (abbreviation e.g. O-Levels) and 'o' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for commentator that I've seen before include "Critic" , "One who reports on sports event" , "pundit" , "Sports match reporter" , "One describes" .)