Rappers cross about critics (4-8)

I believe the answer is:

door-knockers

I'm a little stuck... Click here to teach me more about this clue!

'rappers' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.

'cross about critics' is the wordplay.
'cross' becomes 'rood' (term for a crucifix).
'about' says the letters should be written in reverse.
'critics' becomes 'knockers' (I've seen this before).
'rood' in reverse letter order is 'door'.
'door'+'knockers'='DOOR-KNOCKERS'

Can you help me to learn more?

I've seen this clue in The Guardian.

Want a hint initially instead of a full solution? Install my app