The Black Cats star is unhappy with his side's performance in the 2-1 loss at Carrow Road and believes the team wasted opportunities to get something out of the match
Steve Bruce's side were beaten 2-1 at Carrow Road, leading to Norwich’s first home win back in the top flight.
Richardson thinks the team have let the fans down with their showing and didn't make the most of their possession.
He told safc.com: "We were on a high after the Stoke game, but we didn't play well tonight. We had possession in the first half, but it wasn't effective.
"It's a shame because we have let the fans down and I am sorry for that."
The former Manchester United man scored late on but couldn't hide his disappointment with the result.
"I was pleased to score but the result overall is very disappointing," he said.
"I thought we were good enough to get back into the game, but it wasn't to be.
"In the second half, we didn't put our foot on the ball at all. We didn't get in possession, whereas at least we had some of the ball in the first half.
"We still had chances in the second half, though. Connor [Wickham] had a chance with a header and was unlucky - on another day that would have gone either side of the keeper and gone in."