What spectators sit on to support teams (9)
I believe the answer is:
backsides
'what spectators sit' is the definition.
I can't judge whether this definition defines the answer.
'on to support teams' is the wordplay.
'on' is a charade indicator (letters next to each other).
'to support' becomes 'back' (to back is to support or endorse).
'teams' becomes 'sides' (eg football sides).
'back' next to 'sides' is 'BACKSIDES'.
Can you help me to learn more?
(Another definition for backsides that I've seen is " seats".)