Likely to toy with victim, rat trapping brown relative of his? (3-3-5)
I believe the answer is:
cat-and-mouse
'likely to toy with victim' is the definition.
I can't judge whether this defines the answer.
'rat trapping brown relative of his?' is the wordplay.
'rat' becomes 'cad' (I've seen this in other clues).
'trapping' is an insertion indicator.
'brown' becomes 'tan' (tan is a kind of brown).
'relative of his?' becomes 'mouse' (I can't justify this - if you can you should give a lot more credence to this answer).
'cad' placed around 'tan' is 'catand'.
'catand'+'mouse'='CAT-AND-MOUSE'
Can you help me to learn more?
(Another definition for cat-and-mouse that I've seen is " (Of tactics) waiting and watching for the moment to strike".)