Everybody is in endless rush in US city (6)
I believe the answer is:
dallas
'us city' is the definition.
(I've seen this before)
'everybody is in endless rush' is the wordplay.
'everybody' becomes 'all' (all people).
'is in' indicates putting letters inside.
'endless' means to remove the last letter.
'rush' becomes 'dash' (dashing is a kind of rushing).
'dash' with its last letter removed is 'das'.
'all' placed within 'das' is 'DALLAS'.
'in' acts as a link.
(Other definitions for dallas that I've seen before include "Mysteriously, all sad in the US city" , "Texan city and TV series of the 80s" , "City where J. F. Kennedy was assassinated" , "city built on oil" , "The Ewing family saga" .)