Kagiso Rabada's shoulder brush with and send-off of Steven Smith could end up attracting the attention of match officials, already alert to such moments in a series that is - even at just over one-Test old - not short of them. Nathan Lyon, David Warner and Quinton de Kock have all been sanctioned after the first Test, though potential consequences for Rabada could be graver. The match referee, Jeff Crowe, is expected to make a ruling on the incident on Saturday morning.
Rabada found reverse swing shortly before tea and angled a length ball in at middle stump towards a shuffling Smith, who was struck on the back pad, in front of middle stump. Smith was given out on-field by Kumar Dharmasena and, in celebration, Rabada continued in his follow-through, shouting "Yes, yes," in Smith's direction. With Smith directly in his line of movement, Rabada's shoulder made contact with that of the Australian captain.
Smith reviewed but began walking as soon as replays showed where he had been hit. Rabada went on to take four more wickets, claiming five in the space of 18 balls, either side of the tea interval, to scythe through Australia's middle order, and made considerable use of the reverse-swinging ball. He also had a small word with Mitchell Starc, the last of the five wickets to fall.
Rabada came into this fixture already on notice - he currently has five demerit points to his name and another three will see him sit out two Tests; a tally of eight demerit points within a 24-month period attracts such a penalty as per ICC rules.
Rabada's rap sheet dates back to February last year when he picked up three demerit points and a 50% match fee fine after a shoulder shove to Sri Lanka's Niroshan Dickwella in an ODI. He then earned a another demerit point in July, when he swore at Ben Stokes after dismissing him at Lord's during the first Test between South Africa and England. Rabada missed the second Test at Trent Bridge as a result; four demerit points lead to a ban of one Test or two limited-overs games, whichever comes first, while eight demerit points result in double the penalty. Each demerit point stays on a player's record for a period of 24 months, staying active even after the four-point threshold is broken.
This year, Rabada added a fifth point to his name when he gave Shikhar Dhawan a send-off during an ODI at St George's Park last month. Replays showed Rabada waving goodbye to Dhawan and then telling him to "f*** off".
While the punishment for both his verbal transgressions amounted to only one demerit point, physical contact, which is deemed inappropriate and deliberate, falls under a Level 2 offence. If found guilty of such a charge, a minimum of three demerit points are applied. That would take Rabada to eight, which would mean he misses the rest of the Australia series.
This series has already been marred by three instances of players committing code of conduct offences. Lyon was fined 15% of his match fee and received one demerit point for dropping a ball close to AB de Villiers when he was run out in Durban, Warner was fined 75% of his match fee and earned three demerit points for his role in the stairwell saga that has dominated headlines between Tests, and de Kock was fined 25% of his match fee and earned one demerit point for his part in the same.
Firdose Moonda is ESPNcricinfo's South Africa correspondent