My view is that Haaland is a bit taller than Richards and he has the ability to jump higher than most making him very difficult to defend against. We should have blocked the cross.
Mateta should study Haaland's technique as his offensive heading is poor (but he is good at defending crosses)
When Haaland pull off to the back post Richards must have known it was his responsibility to mark him. When the cross came in Richards took a step forward whilst Haaland took a step backwards creating the space for a free header.
Richards should have just stuck to his man and made it difficult to get a header in, even if he couldn't win it.
Richards is a very good defender and has improved massively. However, against the very best he comes up slightly short, as he showed this weekend.