Old inclination started and ran riot (8)
I believe the answer is:
rampaged
'ran riot' is the definition.
(I've seen this before)
'old inclination started' is the wordplay.
'old' becomes 'aged' (similar in meaning).
'inclination' becomes 'ramp' (an inclined surface).
'started' says to put letters next to each other.
'aged' after 'ramp' is 'RAMPAGED'.
'and' acts as a link.
(Other definitions for rampaged that I've seen before include "ran amok" , "Rushed wildly" , "Went berserk" , "ran riot" , "Charged" .)