The Professional Footballers' Association called for a government inquiry into racism in football after Chelsea's 2-0 Premier League win at Tottenham on Sunday was marred by alleged racist comments from the crowd, the latest in a string of recent incidents.
Chelsea manager Frank Lampard said the problem needed "to be dealt with strongly" and Tottenham promised "a thorough investigation" after referee Anthony Taylor halted play during the second half when Antonio Rudiger complained of hearing monkey noises from spectators.
Moments earlier the Chelsea defender had been involved in a second-half clash with Son Heung-min that saw the South Korean sent off.
Shortly after the stoppage, an announcement made over the public address system warned that "racist behaviour among spectators is interfering with the game" and Taylor spoke to both managers, Lampard and Jose Mourinho.
Two further public address announcements followed after play was resumed.
"It's just such a shame that racism still exists in 2019. When will this nonsense stop?" Rudiger tweeted.
- 'There must be witnesses' -
"I really hope that the offenders will be found and punished soon, and in such a modern football ground like the Tottenham Hotspur Stadium with dozens of TV and security cameras, it must be possible to find and subsequently punish them.
"If not, then there must have been witnesses in the stadium who saw and heard the incident."
The PFA said in a statement late Sunday: "We are disgusted and dismayed that once again, a Premier League fixture has been tainted by abuse from the stands towards players.
"It has become clear that football players are on the receiving end of the blatant racism that is currently rife in the UK, but they are not alone.
"Racist abuse in football is not just an issue for black and ethnic minority players, it is an issue for everyone who loves the game.
"The PFA calls for a government inquiry into racism and the rise in hate crime within football."
- Rising problem -
Two weeks ago a man was identified and arrested for an alleged racist gesture caught on TV cameras during the Manchester derby between City and United, while an Italy's Serie A apologised last week after an anti-racism campaign featuring posters with images of monkeys was widely condemned.
UEFA chief Aleksander Ceferin earlier this month pledged European football's governing body was working to tackle the rising problem after a spate of incidents across the continent including the hurling of racist abuse at England players during a match in Bulgaria.
But Ceferin accused British Prime Minister Boris Johnson of fuelling the problem.
"When a politician that calls women with burqas post boxes or mailboxes then says publicly that he condemns you UEFA (for not tackling racism) -- do you reply to that? Do you believe it's honest? Come on," said Ceferin.
Former Manchester United player Gary Neville also accused top UK politicians.
"We've just had a general election in this country with both main parties and the leaders of both main parties accused constantly of fuelling racism and accepting racism in their parties," said Neville on Sky Sports.
"If it's accepted in the highest office in the country, we're not talking at a micro-level."
"Maybe we have to empower the players to walk off the pitch and stop the entertainment while it is happening," he added.
- 'Accepted in highest level' -
The ugly scenes overshadowed the Willian double that gave Lampard a memorable triumph at the expense of his former Chelsea manager Mourinho.
Lampard insisted there was never any question of his team leaving the pitch in protest.
"Of course, we know there is a protocol," he said. "It needs to be dealt with strongly."
Tottenham manager Mourinho condemned racism but still took a swipe at Rudiger, accusing him of play-acting by clutching his ribs to get Son sent off.
"I hate racism in society, I hate racism in football. I'm disappointed that things like that can happen. The club is a very proud club in this kind of situation and internally we will try to deal with it," he said.
Lampard outwitted his old boss so effectively that Chelsea dominated from start to finish.
Willian's superb opener was followed by a clinical penalty from the Brazilian as Chelsea held onto fourth place and moved six points clear of seventh-placed Tottenham.
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