Was leader over summer, having run (8)
I believe the answer is:
laddered
'having run' is the definition.
I can't tell whether this definition defines the answer.
'was leader over summer' is the wordplay.
'was leader' becomes 'led' (a leader leads people).
'over' means one lot of letters goes inside another.
'summer' becomes 'adder' (someone who adds or does sums).
'led' going around 'adder' is 'LADDERED'.
Can you help me to learn more?
(Other definitions for laddered that I've seen before include "(Of tights or stockings) having a run" , "ran" , "Guided around snake" , "23 25 [WARDROBE MALFUNCTION] perhaps?" , "Descriptive of a stocking with a run" .)