Possible Clues:

• Going to fall for an adder upper, perhaps
• Scarcely get along as 11 across
• How after tea the beast might hardly walk
• Having no feet, an adder might begin to fall
• Having no legs, this sort of adder can hardly walk
• Walk unsteadily as is about to fall
• Summer's sway
• Dodder
• Scrap dealer
• Perhaps an adder might fall for this