A Newcastle football fan has been removed from the jury of a sex assault trial after confessing he couldn't give someone from Sunderland a fair trial so soon after Paolo di Canio's team beat Newcastle 3-0.

The juror admitted his prejudice to court staff and was brought before Judge Penny Moreland at Newcastle crown court on Monday, it emerged on Friday.

The unnamed juror is alleged to have called the defendant, David Blake from Sunderland, a "Mackem rapist" 24 hours after the Tyne and Wear derby earlier this month, which was followed by violent scenes from some fans. Mackem, a term for people from Sunderland, is also used for Sunderland fans.

As a result, before hearing any evidence from the witness box, the juror was removed.

A spokeswoman for the judiciary said on Friday: "I can confirm that the judge did discharge a juror. Because the trial was at a very early stage the judge then discharged the remaining 11 jurors and a new jury was empanelled. The juror had himself approached a member of court staff and made the comment which in the judge's view made him unsuitable to try the defendant."

Jurors are given a clear warning by judges at the start of every case that they must try defendants on the evidence they hear in court and nothing else.

Blake's trial was halted after half a day, meaning the victim, who was anxiously waiting to give evidence, faced a delay while a new jury was sworn in. As a result of the false start Blake's victim had to relive her ordeal by watching her video evidence twice as the prosecution's opening was repeated for the new jury.

Blake was eventually found guilty of raping the woman, who had fallen asleep in a spare bed, alone, after a party at a flat. He will be sentenced next month but was warned to expect a prison term.

In a separate case, the attorney general announced on Wednesday that a man called Kasim Davey would be prosecuted for contempt of court after allegedly writing on Facebook that he wanted to "fuck up a paedophile" during the trial of a convicted child sex offender.

Davey was discharged as a juror in the trial in December when he wrote on Facebook: "Woooow I wasn't expecting to be in a jury Deciding a paedophile's fate, I've always wanted to Fuck up a paedophile & now I'm within the law!"

He denied posting the message – which is in breach of laws on contempt of court – when initially questioned by the judge at Wood Green crown court in London. Davey was a juror at the trial of Adam Kephalas, a convicted child-sex offender who was given a suspended 12-month prison sentence in January this year.