Old statesman exercised coercion on leaving (6)
I believe the answer is:
Here is my best explanation:
'old statesman' is the definition.
'exercised coercion on leaving' is the subsidiary indication.
'exercised' indicates an anagram.
'leaving' indicates named letters should be taken away.
'coercion' with 'on' removed is 'coerci'.
'coerci' with letters rearranged gives 'cicero'.
(Other definitions for cicero that I've seen before include "Roman lawyer", "Roman orator and master of prose", "Famous Roman orator", "roman", "Statesman from Rome", "Philosopher", "One-time consul", "wartime spy", "Marcus Tullius -, Roman consul, orator and writer" and "Old Roman statesman and orator".)