Mattock, 20, was given a suspended sentence for punching two men and two women in Liquid Envy in Church Gate, Leicester, on August 30, 2009.
Leicester Crown Court heard that Mattock, who was 19 at the time, hit out after he was given "grief" over a transfer from Leicester.
The Leicester-born player, who is currently sidelined by an ankle injury, joined West Brom last August for £1million, causing anger among many Leicester fans.
The defender, of Grove Road, Leicester, pleaded guilty to a charge of affray at Leicester Crown Court in July.
On Thursday, at the same court, he was handed 10 months' detention, suspended for two years. He was also ordered to complete 150 hours of unpaid work, and to pay £1,500 costs.
Judge Michael Pert QC told the footballer: "You plainly worked hard at your craft and were a successful professional footballer.
"The plain fact of the matter is you were earning what most people would regard as a king's ransom.
"If the price of that is to take some stick in a nightclub in your home city when you had left Leicester for another club, frankly you should have been able to handle it.
"It's plain from what we have seen that you were not able to handle whatever was said to you on that occasion and your behaviour was disgraceful."