Main tempo set for show (9)
I believe the answer is:
pantomime
'show' is the definition.
(I've seen this before)
'main tempo set' is the wordplay.
'set' is an anagram indicator (instruction to set the letters).
'main'+'tempo'='maintempo'
'maintempo' anagrammed gives 'PANTOMIME'.
'for' acts as a link.
(Other definitions for pantomime that I've seen before include "Farcical situation" , "Traditional Christmas stage show with Dame" , "Theatrical entertainment (usually at Christmas)" , "'He's behind you' entertainment" , "Cross-dressing theatrical" .)