Race with some not quite finishing, all collapsing (6)
I believe the answer is:
slalom
'race' is the definition.
('slalom' means to move in a zigzag)
'some not quite finishing all collapsing' is the wordplay.
'not quite' means to remove the last letter.
'finishing' says to put letters next to each other.
'collapsing' is an anagram indicator.
'some' with its final letter removed is 'som'.
'som'+'all'='somall'
'somall' is an anagram of 'SLALOM'.
'with' is the link.
(Other definitions for slalom that I've seen before include "Type of ski race" , "Downhill ski-race over a winding course" , "Skiing obstacle race" , "Windy skiing event" , "Winding ski-run" .)