Dummy on farm runs in silly cow races (9)
I believe the answer is:
scarecrow
'dummy on farm' is the definition.
'scarecrow' can be an answer for 'dummy' (thesaurus). I am not sure about the 'on farm' bit.
'runs in silly cow races' is the wordplay.
'runs' becomes 'r' (cricket abbreviation).
'in' indicates putting letters inside.
'silly' indicates anagramming the letters.
'cow'+'races'='cowraces'
'cowraces' with letters rearranged gives 'scarecow'.
'r' going into 'scarecow' is 'SCARECROW'.
Can you help me to learn more?
(Other definitions for scarecrow that I've seen before include "Bird discourager" , "One in 5d's party" , "Badly dressed person" , "6 [FRIEND OF DOROTHY]" , "Bird frightener" .)