Broad, who was fielding in the covers, appeared to become involved in a heated discussion with du Plessis, after the South Africa captain had been hit on the pads by a throw to the keeper. Du Plessis said after the match that he had been "trying to show fight as the leader", as South Africa battled in the face of a hefty fourth-innings target. "It was just myself and Broady having a go," he said.
The match officials subsequently charged Broad with a Level 1 offence, under Article 2.3 of the ICC code of conduct. He was fined 15% of his match fee and now has two active demerit points on his record - following a reprimand for giving Rishabh Pant a send-off at Trent Bridge in 2018.
Vernon Philander and Ben Stokes were both hit with Level 1 penalties during the Wanderers Test, a game that Kagiso Rabada sat out after collecting his fourth demerit point within a two-year period in the third Test at Port Elizabeth. Buttler was found guilty of a Level 1 offence in Cape Town, after being picked up by the stumps mics swearing at Philander.
England won the Test series 3-1, following a 191-run victory in Johannesburg. The tour will also encompass six limited-overs internationals, starting with the first ODI at Newlands on February 4.