Draw animal, filling in only half (7)
I believe the answer is:
lottery
'draw' is the definition.
(I've seen this before)
'animal filling in only half' is the wordplay.
'animal' becomes 'otter' (I've seen this before).
'filling in' is an insertion indicator.
'half' suggests halving the letters.
'only' cut in half is 'ly'.
'otter' placed into 'ly' is 'LOTTERY'.
(Other definitions for lottery that I've seen before include "The random drawing of numbers from a drum" , "Sweepstake" , "Chance process" , "Matter of chance" , "Random prize game" .)