Mad relatives: one may floor the unwary (6,4)
I believe the answer is:
banana skin
'one may floor the unwary' is the definition.
(you might trip over a banana skin)
'mad relatives' is the wordplay.
'mad' becomes 'bananas' (I've seen this in another clue).
'relatives' becomes 'kin' (I've seen this in another clue).
'bananas'+'kin'='BANANA SKIN'
(Other definitions for banana skin that I've seen before include "Potential source of slip-up" , "potential trouble" , "something to cause embarrassment" , "pedestrian problem" , "One to slip on" .)