One may have a number of bowlers not being used (8)
'bowlers not being used' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.
'one may have a number' is the wordplay.
I cannot really understand how this works, but
'one' could be 'an' (I've seen this in other clues) and 'an' is located in the answer.
'a' is within the answer.
'number' could be 'd' (D is an example) and 'd' is found in the answer.
This may be the basis of clue (or it may be nonsense).
'of' acts as a link.
Can you help me to learn more?
(Another definition for hatstand that I've seen is "Piece of furniture with pegs".)