Races including contest chasing American cars? (9)

'cars?' is the definition.
(runabout is a kind of car)

'races including contest chasing american' is the wordplay.
'races' becomes 'runs' (running is a kind of racing).
'including' is an insertion indicator.
'contest' becomes 'bout' (boxing contest).
'chasing' says to put letters next to each other (some letters chase after others).
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'bout' put after 'a' is 'about'.
'runs' placed around 'about' is 'RUNABOUTS'.