A fan has described the violence that erupted after a Carling Cup match between Birmingham City and local rivals Aston Villa as "like a warzone".
Five people were arrested and 27 hurt after City fans invaded the pitch following their side's 2-1 victory.
Aston Villa fans responded by throwing a flare and ripping up plastic seats at City's St Andrews ground.
Villa fan Rob, from Cheltenham, told BBC Five Live his 11-year-old son was repeatedly spat at during the violence.
He said: "There was a lot of trouble before the game.
"The scenes were really disgraceful.
"My 11-year-old son was spat at repeatedly and there was CS gas used against the police - we were told that by a lady officer on the way out of the ground.
"It's a bit of a warzone really."
A pub outside the ground and parked cars were also vandalised following the quarter-final game.
Supt Steve Graham, from West Midlands Police, said the violence was reminiscent of the 1980s heyday of football hooliganism.
"There are perhaps cops who have been in the job 25 or 30 years who went back to the future there - that's not the face of modern football," he said.
"Everyone was hoping that they would put on a showcase of football in the Second City and that it would be an example we could show around the world with pride."
The trouble came hours before the vote to decide if England will host the 2018 World Cup.
Birmingham City and the FA have said they are investigating the disorder.
The club described the violence as "disappointing" and said officials would be meeting later to investigate the matter further.
Manager Alex McLeish said it threatened to bring English football "back to the dark ages" but said he did not think it would affect England's bid to host the World Cup.
West Midlands Ambulance Service said casualties suffered head, leg and arm injuries and taken to hospital.
Supt Graham said officers got fans off the pitch within about 10 minutes of the game ending but said some "innocent parties" would have been injured outside the ground.
He described it as "mindless and inexcusable".
The FA said it "wholly condemned" the actions of those involved.
The last time Birmingham City and Aston Villa were allowed to play each other in an evening game was seven years ago.
Following clashes between supporters during the 2002-03 season, West Midlands Police insisted all future derbies be played on a Sunday lunchtime.
The Carling Cup draw led to that rule being waived for this game.
http://www.bbc.co.uk/news/uk-england-birmingham-11896282
