Denied it's rubbish on the day (7)
I believe the answer is:
refused
'denied' is the definition.
('refuse' can be a synonym of 'deny')
'on the day' is the wordplay.
'on' becomes 're' (regarding).
'the day' becomes 'fused' (I can't explain this - if you can you should give a lot more credence to this answer).
're'+'fused'='REFUSED'
'it's rubbish' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for refused that I've seen before include "Said no (7)" , "turned down appeal" , "Declined, rejected" , "Was unwilling to accept" , "Not accepted" .)