Shoot small beast crossing river (5)
I believe the answer is:
sprig
'shoot' is the definition.
(I've seen this in another clue)
'small beast crossing river' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'beast' becomes 'pig' (I can't explain this - if you can you should give a lot more credence to this answer).
'crossing' indicates putting letters inside (to cross can mean to go over or around).
'river' becomes 'r' (abbreviation).
'pig' going around 'r' is 'prig'.
's'+'prig'='SPRIG'
Can you help me to learn more?
(Other definitions for sprig that I've seen before include "Small stem taken from a bush or plant" , "Grips with a small branch" , "piece of holly" , "Small nail without a head" , "Small branch or shoot" .)