Cameron Bancroft, the Australia opener, was spoken to by the on-field umpires after television cameras captured him holding a foreign object when working on the ball during the second session on day three of the Newlands Test.
A small, yellow object was seen in Bancroft's hands after he had worked on the ball, and he was also captured taking it from his pocket and seeming to place it down his trousers. The footage showed Bancroft seeming to rub the rough side of the ball, the opposite side to which he would usually be trying to shine on his trousers, as is permitted under ICC playing conditions. He appeared to put the object down his pants apparently after being spoken to by the substitute Peter Handscomb, who had come on to the field after speaking to coach Darren Lehmann over walkie talkie. Lehmann seemed to speak to Handscomb after footage of Bancroft working on the ball was shown on the TV screens at the ground.
The umpires Nigel Llong and Richard Illingworth were then seen speaking with Bancroft, though they did not choose to change the ball nor penalise the Australians five runs - the statutory on-field penalty for illegally changing the condition of the ball.
When Bancroft spoke to the umpires, he was shown holding a bigger, black cloth rather than the small yellow object he had earlier seemed to place down his trousers. Both South African and Australian commentators on the host broadcaster, SuperSport, said Bancroft's actions looked suspicious. "It is very suspicious. There is no doubt about that," Allan Border said. "If you're caught doing the wrong thing, you've got to pay the penalty."
The former South Africa captain Graeme Smith said he was surprised the umpires had not changed the ball. "In my opinion I think he's tampered with the ball and used an object to do that," Smith said. "It does look like it's a bit of sandpaper. The footage doesn't look good. I'm quite amazed the umpires haven't done anything with the ball. The footage is quite damning.
"If it is proved that what has gone on in the footage is correct then some tough questions have to be asked of Steve Smith and Darren Lehmann. I think there is a lot of questions that need to be answered and Australia need to answer them. For me it's quite obvious that he's doing something with the ball and the umpires need to do something about it."
Shane Warne, meanwhile, said it was unlikely that Bancroft had acted alone, without the knowledge of his captain and coach. "You've got to own up and say what was it that you were hiding," Warne said. "You can't have that in the game. We've got to get to the bottom of it. The Aussies have to be honest and say 'this is how it happened'." I don't have any issue with anyone if they are sucking on a mint or chewing some gum, then that's just natural saliva.
"But if you use a foreign object and it tampers with the ball then that has to be seriously looked at. Let's get to the bottom of what it is and how did it happen. And it's not fair to nail Cameron Bancroft on it either. I don't think he would have made that decision by himself. We've got to get to the bottom of it. You know when you get caught you've got to own up and be honest. The Aussies have to be honest and say this is how it happened."
Australia's bowlers had been able to gain pronounced reverse swing on day three in Cape Town, though South Africa continued to build their second-innings lead. Questions about ball tampering have been raised throughout the series, where reverse swing has been a consistent theme.
Warner was highlighted for the bandages on his hand in Port Elizabeth, the result of numerous finger injuries suffered while batting in the past, and on day one at Newlands the fast bowler Pat Cummins was seen to tread on the ball, though the umpires did not view it as deliberate, and saw no reason to penalise the Australians or change the ball.
Earier in the series, the Australia coach Darren Lehmann said both sides would try various "techniques" to get the ball to reverse swing. The pitch and wicket square at Newlands has been notably greener than those of Durban and Port Elizabeth, meaning there is less natural roughing up of the ball to be gained.
"Obviously, there are techniques used by both sides to get the ball reverse and that's just the way the game goes," Lehmann said after the Durban Test. "I have no problems with it, simple. You'd have to ask the umpires and ICC about that one [whether it is legal]. I don't mind the ball moving, I have no problems with it at all.
"It makes great viewing as a fan of the game. It's challenging for batters and challenging for bowlers to get it in the right position. If you don't get it in the right position, you saw [on day four] we didn't bowl very well for about two or three hours. It reversed and we couldn't get it right. They scored very heavily, so you've still got to bowl well."
Daniel Brettig is an assistant editor at ESPNcricinfo. @danbrettig