A female horse was the first faller (4)
I believe the answer is:
adam
'horse was the first faller' is the definition.
I know that 'first' relates to this answer.
'a female' is the wordplay.
'female' becomes 'dam' (dam is a kind of female).
'a'+'dam'='ADAM'
Can you help me to learn more?
(Other definitions for adam that I've seen before include "First person" , "Eves husband" , "Eden inhabitant" , "neoclassical style" , "Eden man" .)