Selecting without a number stampeding (9)
I believe the answer is:
panicking
'stampeding' is the definition.
('panic' can be a synonym of 'stampede')
'selecting without a number' is the wordplay.
'selecting' becomes 'picking' (picking is a kind of selecting).
'without' indicates putting letters inside ('without' can be similar in meaning to 'outside').
'number' becomes 'n' (n can represent any number).
'a'+'n'='an'
'picking' enclosing 'an' is 'PANICKING'.
(Other definitions for panicking that I've seen before include "Acting rashly through fear" , "Losing one's head" .)