This stops the rider from being footloose (7)
I believe the answer is:
stirrup
'this stops' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'the rider from being footloose' is the wordplay.
I cannot quite understand how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is present in the answer.
'being' could be 'sir' (Sir is an example) and 'sir' is present in the leftover letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for stirrup that I've seen before include "Equine foot rest" , "Jockey's foot support" , "supporter?" , "Rider's foothold" , "one puts the boot into" .)