Are possibly about a foot behind (5)
I believe the answer is:
after
'behind' is the definition.
(eg after or behind someone in a queue)
'are possibly about a foot' is the wordplay.
'possibly' indicates an anagram.
'about' means one lot of letters goes inside another.
'a foot' becomes 'ft' (abbreviation).
'are' is an anagram of 'aer'.
'aer' going around 'ft' is 'AFTER'.
(Other definitions for after that I've seen before include "Behind; seeking" , "Subsequently" , "At a later time or behind" , "since" , "Pursuing" .)