Rebels imprisoning family with son showing dangerous attitude (9)
I believe the answer is:
riskiness
'dangerous attitude' is the definition.
'rebels imprisoning family with son' is the wordplay.
'rebels' becomes 'rises' ('rise' can be a synonym of 'rebel'**).
'imprisoning' indicates putting letters inside.
'family' becomes 'kin' ('kin' can be a synonym of 'family').
'with' means one lot of letters go next to another.
'son' becomes 's'.
'rises' going around 'kin' is 'riskines'.
'riskines'+'s'='RISKINESS'
'showing' acts as a link.
(Another definition for riskiness that I've seen is " Level of danger".)