Rodent's limb grabbed by cat from behind (6)
I believe the answer is:
marmot
'rodent's' is the definition.
(marmot is a kind of rodent)
'limb grabbed by cat from behind' is the wordplay.
'limb' becomes 'arm' (arm is a kind of limb).
'grabbed by' means one lot of letters goes inside another (inserted letters are grabbed inside).
'cat' becomes 'tom' (a tom is a male cat).
'from behind' is a reversal indicator.
'tom' written backwards gives 'mot'.
'arm' going inside 'mot' is 'MARMOT'.
(Other definitions for marmot that I've seen before include "Coarse-furred burrowing rodent" , "Stout, burrowing rodent" , "Small burrowing animal of the squirrel family" , "Furry burrowing rodent" , "wild rodent" .)