Over Tannoy, makes illegal announcement about match (5)
I believe the answer is:
banns
'announcement about match' is the definition.
I can't judge whether this defines the answer.
'over tannoy makes illegal' is the wordplay.
'over' is an insertion indicator.
'tannoy' becomes 'n' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'makes illegal' becomes 'bans' (I've seen this in another clue).
'n' inserted inside 'bans' is 'BANNS'.
Can you help me to learn more?
(Other definitions for banns that I've seen before include "Notice of marriage read in church" , "Pre-wedding notice" , "Notice of a wedding" , "Public announcement read in church of forthcoming marriage" , "Proclamation of intended marriage" .)