Spider natural at running (9)
I believe the answer is:
tarantula
'spider' is the definition.
(I know that tarantula is a type of hunting spider)
'natural at running' is the wordplay.
'running' indicates an anagram.
'natural'+'at'='naturalat'
'naturalat' is an anagram of 'TARANTULA'.
(Other definitions for tarantula that I've seen before include "small, venomous creature" , "hairy creature" , "A big hairy spider" , "spider to appear" , "A large hairy tropical spider" .)