A live bar performance is a bit up and down (8)
I believe the answer is:
variable
'bit up and down' is the definition.
Both the answer and definition are adjectives. Maybe they are linked in a way I don't understand?
'a live bar performance' is the wordplay.
'performance' indicates anagramming the letters.
'a'+'live'+'bar'='alivebar'
'alivebar' is an anagram of 'VARIABLE'.
'is a' acts as a link.
Can you help me to learn more?
(Other definitions for variable that I've seen before include "Liable to change" , "Mutable" , "can be changed" , "Subject to change" , "Fickle" .)