Target some Plantagenet's supporter? Not good! (4,5)
I believe the answer is:
aunt sally
'target' is the definition.
(I've seen this before)
'some plantagenet's supporter? not good' is the wordplay.
I cannot really see how this works, but
'some' could be 'a' and 'a' is present in the answer.
'supporter?' could be 'ally' (an ally is a friend or supporter) and 'ally' is located in the answer.
'not' could be 'nt' (synonyms) and 'nt' is located in the answer.
The remaining letters 'us' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for aunt sally that I've seen before include "Fairground game - target for insults" , "Family member" , "object of abuse" , "Lusty Lana as target of criticism or missiles" , "Female relation used as a target in throwing game" .)