After dismissing Steve Smith on Friday in Port Elizabeth, Rabada appeared to intentionally bump into the Australia captain with his shoulder.
Rabada is no stranger to improper behaviour, he now has five demerit points to his name and another three will see him sit out two Tests as a tally of eight demerit points within a 24-month period warrants such a penalty, per ICC rules.
Smith whirled around at Rabada after the paceman made the same kind of avoidable contact that resulted in him being fined 50 per cent of his match fee and handed three demerit points for a run-in with Sri Lanka's Niroshan Dickwella in February a year ago.
Rabada now has five demerit points to his name, having picked up a third sanction by the ICC in the past 12 months with his send off of India's Shikhar Dhawan in the fifth match of their one-day series last month.
The aftermath of his first wicket, that of Australian captain Steve Smith, could come under scrutiny at the end of an emotion-charged week when an altercation between Australia's David Warner and South Africa's Quinton de Kock stole much of the attention from Australia's 118-run win in the first Test in Durban. He served a one-Test ban in England past year.
Vernon Philander made light of his teammate's misdeed after play on day one, saying "I don't even recall there being a send-off". "I have spoken to him a few times about it, to try and get him to relax a bit", pace icon Michael Holding told ESPNcricinfo.
Previous year he was found guilty of deliberate physical contact with Sri Lanka's Niroshan Dickwella and was given three demerit points.
"Sometimes there is a fine line whether to celebrate too hard".
"He would leave a massive hole, he's a big part of this bowling line up".
Rabada's running battle with the tourists continued when he was sent out as nightwatchman late in the day.
As a result of this, Cricket Australia (CA) asked their players to tone down the aggression and be nice in the remaining three matches after seeing what happened between Warner and de Kock.
Australia were 182 for eight when Starc was out but wicketkeeper Tim Paine batted well with the last two batsmen, Lyon and Josh Hazlewood as the last two wickets added 61 runs.