Help Gran out, capturing a marsupial (9)
I believe the answer is:
phalanger
'marsupial' is the definition.
(I know that Phalanger is a type of marsupial)
'help gran out capturing a' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'capturing' is an insertion indicator.
'help'+'gran'='helpgran'
'helpgran' with letters rearranged gives 'phlanger'.
'phlanger' enclosing 'a' is 'PHALANGER'.
(Other definitions for phalanger that I've seen before include "Little Aussie's" , "may be flying in Australia" , "Lemur-like creature" , "Marsupial" .)