Condition of faller at Becher's Brook, say (5)
I believe the answer is:
rider
This clue is a double definition.
'condition' is the first definition.
(I've seen this before)
'faller at becher's brook say' is the second definition.
(fence in the Grand National horserace)
'of' acts as a link.
(Other definitions for rider that I've seen before include "Possibly cavalier" , "Supplement to verdict" , "One who's got up" , "One may be saddled" , "Added proviso" .)