Bounder cross when bottom kicked (3)
I believe the answer is:
roo
'bounder' is the definition.
(short for kangaroo, something which bounds)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for roo that I've seen before include "young skipper" , "Wild animal" , "Kanga's son (Pooh)" , "companion of Pooh" , "Jumping marsupial" .)