Worst and best refuelling place (3,4)
I believe the answer is:
pit stop
'refuelling place' is the definition.
(place where cars are refuelled in motor racing)
'worst and best' is the wordplay.
'worst' becomes 'pits' (I've seen this in another clue).
'and' is a charade indicator (letters next to each other).
'best' becomes 'top' (top can mean the very best).
'pits'+'top'='PIT STOP'
(Other definitions for pit stop that I've seen before include "Break for fuel etc." , "Break for refuelling" , "When tripping, break" , "part of the race" , "Break during motor race" .)