Alternate reel (7)
I believe the answer is:
Here is my best explanation:
This clue is a double definition.
'alternate' is the first definition.
'reel' is the second definition.
('stagger' can be a synonym of 'reel')
(Other definitions for stagger that I've seen before include "Reel; arrange so as to be out of line", "Pitch", "Walk as though in danger of falling", "Astound", "Walk as if about to fall", "Totter", "move by someone under the table?", "bowl over", "Reel about; shock" and "Reel; amaze".)