As a rule, not many get involved in it (9)
I believe the answer is:
oligarchy
'it' is the definition.
The definition suggests a singular noun which matches the answer.
'as a rule not many get involved' is the wordplay.
I cannot quite see how this works, but
'a' is present in the answer.
'rule' could be 'r' (legal abbreviation) and 'r' is present in the answer.
'not' could be 'o' (I've seen this in other clues) and 'o' is located in the answer.
'many' could be 'l' and 'l' is located in the answer.
This explanation may well be incorrect...
'in' acts as a link.
Can you help me to learn more?
(Other definitions for oligarchy that I've seen before include "a few men in government" , "Government by small elite" , "Form of government with power held by a few" , "Rule of the few" , "Political system of government by a few people" .)