Switching starters, badger old woman for bottle (6)
I believe the answer is:
magnum
'for bottle' is the definition.
(magnum is a kind of bottle)
'switching starters badger old woman' is the wordplay.
I cannot quite see how this works, but
'woman' could be 'mag' and 'mag' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for magnum that I've seen before include "Double-sized wine bottle" , "Large bottle of champagne, twice normal size" , "Just one bottle of champagne?" , "1.5 litre wine bottle" , "1 1/2 litre champagne bottle" .)