Fairground attractions free every Saturday at the outset (5)
I believe the answer is:
rides
'fairground attractions' is the definition.
(fairground rides)
'free every saturday at the outset' is the wordplay.
'free' becomes 'rid' (to be free of something is to be rid of it).
'at the outset' indicates taking the first letters (the outset is the beginning).
The initial letters of 'every saturday' is 'es'.
'rid'+'es'='RIDES'
(Other definitions for rides that I've seen before include "Comes through" , "Trips" , "Dries up and travels" , "Theme park attractions" , "Travels on something" .)