Upstanding Conservative chasing cat with medium-sized balls (8)
I believe the answer is:
tommyrot
'upstanding conservative chasing cat with medium-sized balls' is the definition.
I can't judge whether this definition defines the answer.
'upstanding conservative chasing cat with medium-sized' is the wordplay.
'upstanding' shows that the letters should be reversed in order.
'conservative' becomes 'tory' (informal term for a Conservative Party member).
'chasing' means one lot of letters go next to another (some letters chase after others).
'cat with' becomes 'tom' (a tom is a male cat. I am not sure about the 'with' bit.).
'medium-sized' becomes 'm' (clothes size).
'tory' back-to-front is 'yrot'.
'tom'+'m'='tomm'
'yrot' put after 'tomm' is 'TOMMYROT'.
Can you help me to learn more?
(Other definitions for tommyrot that I've seen before include "Slangy nonsense from Thomas?" , "Bunk" , "Balderdash, bilge" , "tosh" , "Nonsense, rubbish - ask informal Thomas" .)