Almost spear adult beast (6)
I believe the answer is:
impala
'beast' is the definition.
(I've seen this before)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for impala that I've seen before include "Spectacular jumper" , "prodigious bounder" , "Leaping antelope" , "horned beast" , "Big game" .)