Faf du Plessis, South Africa's captain, could be in trouble with the match referee after appearing to make physical contact with Jos Buttler on the fourth afternoon in Johannesburg.

With du Plessis and Rassie van der Dussen batting together for more than 30 overs on a brutally hot day, England appeared to be growing increasingly frustrated with the lack of movement they were generating from the ball and, it seemed, du Plessis' habit of picking the ball up after playing a stroke and returning it to the fielders.

At one stage, du Plessis was hit on the pads by a throw from Sam Curran, who was fielding at mid-on. That appeared to lead to an exchange of words between du Plessis and several of the fielding side. As the players converged, du Plessis appeared to deliberately walk into Buttler before continuing his verbal altercation with Stuart Broad.

After the game, with South Africa beaten by 191 runs, du Plessis played down the incident, saying he was just trying to show fight and did not realise he had come into contact with Buttler.

"It's part of my character," he said. "I am always involved in a little bit of something somewhere in the game. Trying to show that fight as the leader the team, that you don't stand back. It's not like I am looking for it. It just happens. He said something to me and I said something back.

"I don't think we knew we touched each other. It was just myself and Broady having a go. He [Buttler] was just trying to get between myself and him. There was no malicious thing. He was trying to diffuse the situation. He didn't do anything wrong there. It was just words from Broady."

While the contact was far from violent, the ICC's code of conduct states that "any form of inappropriate physical contact is prohibited in cricket. Without limitation, players will breach this regulation if they deliberately, recklessly and/or negligently walk or run into or shoulder another player or umpire."

Such an incident is considered either a Level 1 or Level 2 offence and carries a maximum penalty of four demerit points, which would also bring an automatic suspension. It may not help du Plessis' case that he is an experienced player and his side's captain. As such, the match referee may expect him to set an example.

England's captain, Joe Root, was sympathetic, however, describing it as a moment of "handbags".

"I thought Faf was trying to use it as an opportunity to get himself going and get himself in the contest and my worry was that it was going to work in his favour," he said. "There was absolutely nothing. It was handbags. Given what's happened in this series, it may become a big thing but it was absolutely nothing."

Moments after the incident, du Plessis' miserable series was ended when a delivery from Ben Stokes kept horribly low and ricocheted into the stumps of a bottom edge. It meant du Plessis had failed to reach 40 in the entire series and took his side close to a 3-1 home defeat. Speculation is rife that this will be du Plessis' final Test as captain and possibly his final Test as a player.

"It happens, that's not me outside my bubble," du Plessis added. "It just got a bit heated. That's not out of my character. If you say something towards me, I will say something back. It doesn't cause me to concentrate less. They got a ball to stay low."

Buttler attracted the ire of the South Africa players for abusing Vernon Philander earlier in the series. Buttler was fined 15% of his match fee and received one demerit point for the episode. Philander, Stokes and Kagiso Rabada have also been punished for disciplinary issues during the Tests.

George Dobell is a senior correspondent at ESPNcricinfo