Reports Athletic Club matters (8)
I believe the answer is:
accounts
'reports' is the definition.
('account' can be a synonym of 'report')
'athletic club matters' is the wordplay.
'athletic club' becomes 'AC' (abbreviation).
'matters' becomes 'counts' (count can mean to matter or be significant).
'ac'+'counts'='ACCOUNTS'
(Other definitions for accounts that I've seen before include "Statements of financial transactions" , "Rates" , "Statements concerning money." , "Records of financial transactions (8)" , "Statement of a company's financial affairs" .)