Summons a vehicle back across open ground (8)
I believe the answer is:
subpoena
'summons' is the definition.
(legal summons)
'a vehicle back across open ground' is the wordplay.
'vehicle' becomes 'bus' (bus is a kind of vehicle).
'back' shows that the letters should be reversed in order.
'across' means one lot of letters goes inside another.
'ground' is an anagram indicator ('grind' the letters into a new form).
'a'+'bus'='abus'
'abus' reversed gives 'suba'.
'open' with letters rearranged gives 'poen'.
'suba' enclosing 'poen' is 'SUBPOENA'.
(Other definitions for subpoena that I've seen before include "Writ to compel a witness to attend court" , "Hearing reminder" , "Writ commanding appearance in court" , "Court-attendance order" , "A summons to attend court case" .)