Badger's behind, not in hollow (4)
I believe the answer is:
rout
'hollow' is the definition.
(routing is a kind of hollowing)
'badger's behind not in' is the wordplay.
'behind' suggests the final letters.
'not in' becomes 'out' ('out' is the opposite to 'in').
The last letter of 'badger' is 'r'.
'r'+'out'='ROUT'
(Other definitions for rout that I've seen before include "Defeat utterly" , "Act like a pig" , "tumultuous crowd" , "Vanquish; thrash" , "Total defeat in battle" .)