Rep larks around, displaying firework (8)
I believe the answer is:
sparkler
'firework' is the definition.
(sparkler is a kind of firework)
'rep larks around' is the wordplay.
'around' indicates an anagram.
'rep'+'larks'='replarks'
'replarks' is an anagram of 'SPARKLER'.
'displaying' acts as a link.
(Other definitions for sparkler that I've seen before include "Eg, a diamond" , "Firework - precious stone" , "Hand-held firework" , "Possibly brilliant" , "Firework or diamond ring" .)