Left with snake, run (6)
I believe the answer is:
ladder
'run' is the definition.
(both can mean a rip in tights)
'left with snake' is the wordplay.
'left' becomes 'l' (common abbreviation).
'with' means one lot of letters go next to another.
'snake' becomes 'adder' (adder is a kind of snake).
'l'+'adder'='LADDER'
(Other definitions for ladder that I've seen before include "snag in hose" , "Climbing structure" , "A run in a stocking" , "Vertical run in tights" , "something that can send you in the opposite direction?" .)