Headlong rush (8)
'headlong rush' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for stampede that I've seen before include "Sudden rush of people" , "Chaotic rush" , "rush for safety maybe" , "Sudden dash of a group of startled animals" , "Headlong rush of a group in panic" .)
(Other definitions for haste that I've seen before include "''Marry in . . . . ., repent at leisure''" , "Rushing (but with less speed?)" , "furious activity" , "Hurriedness" , "More of this can slow you up!" .)