Doctor Who following teams — not the main event (8)
I believe the answer is:
'event' is the definition.
(sideshow is a kind of event)
'doctor who following teams' is the wordplay.
'doctor' indicates anagramming the letters.
'following' says to put letters next to each other.
'teams' becomes 'sides' (eg football sides).
'who' anagrammed gives 'how'.
'how' after 'sides' is 'SIDESHOW'.
'not the main' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for sideshow that I've seen before include "Not the main scene of activity" , "Subordinate production to the main event" , "affair at a fair" , "Unimportant" , "Wished so for minor incident or issue - at fair?" .)