This man is offering shoppers a chance to double their money in an apparently innocent game of chance.
However, police fear it is one of the oldest scams in the book - the "three cup trick".
The Leicester Mercury watched the man, and several people who were believed to be accomplices, invite city centre shoppers to double their £20 bets if they could find a ball hidden underneath one of three matchboxes.
However, it is believed the man uses sleight of hand to ensure he keeps winning.
He turned up yesterday morning at the junction of Halford Street and Granby Street, and later in Humberstone Gate.
On both occasions, he appeared to have at least eight people with him, some apparently acting as look-outs stationed up to 50 yards away.
Others seemed to be passing themselves off as ordinary members of the public having a flutter on the game.
At least two women who played and won while the Mercury was observing walked away with the man when police approached.
A few minutes later, the trio were still together, with others, elsewhere in the city centre.
One gamer, who lost £20 in a single bet, said: "I thought I'd have a go because it's a one-in-three chance and I like a bet every now and then.
"I watched a woman have a couple of goes and she won both times, but then when a police car arrived she walked away with the man who was running the game.
"That cracked it for me, I don't believe this is an innocent game of chance. They appear to be working together to con people."
Another man who watched the gang at work in Humberstone Gate was repeatedly urging people not to be taken in.
He said: "It's the oldest scam in the book and I can't believe people are handing over £20 a time."
Pc Nik Peacock, of city centre police, said officers were determined to disrupt the group by continually moving them on.
The group was committing an offence by running a gambling operation without a licence from the council, he said.
However, officers also suspect the game is rigged.
Pc Peacock said: "People who are not part of the group have faces like thunder when they lose, while the friends of the people behind the game keep smiling because they're not really losing anything."
Police powers to arrest people they suspect of running scams of this nature are limited because it is difficult to prove the act of deception.
Also, it falls to local authorities to prosecute breaches of licensing regulations.
A group suspected of running the same scam were arrested following a joint operation by city police and Leicester City Council last year. The case is still to come to court.
A city council spokesman said: "We would classify this kind of activity as gambling, which they would need to have a licence for."
Max Boden, policy manager at Leicestershire Chamber of Commerce, said: "This is not like having a bet at the races, the three cup trick - or any variation of it - is a scam, and we do not want it in Leicester."