Young beast bit German neighbour (7)
I believe the answer is:
tadpole
'young beast' is the definition.
'bit german neighbour' is the wordplay.
'bit' becomes 'tad' (I've seen this before).
'german neighbour' becomes 'pole' (native of Poland).
'tad'+'pole'='TADPOLE'
(Other definitions for tadpole that I've seen before include "Little creature in water" , "Immature amphibian" , "Baby amphibian" , "Young Kermit" , "wriggler?" .)