Smith in for tough time: du Plessis

Twice convicted of ball tampering, South Africa skipper Faf du Plessis is one of the few people in the world with an insight into what Steve Smith's life is like at the moment.

Du Plessis pleaded guilty to the charge of ball tampering in a 2013 Test. He rubbed the ball on the zipper of his pants pocket and umpires awarded a five-run penalty against the Proteas.

Du Plessis then maintained his innocence in 2016, when footage emerged of him using a mint to help shine the ball during a Test against Australia in Hobart, but he never beat the charge of ball tampering.

The 33-year-old still has the resultant three demerit points on his record from 'mintgate'.

Following the charge from the ICC, Smith will have four demerit points on his record for the next two years, while Australia's skipper will miss the Test that starts on Friday in Johannesburg.

The shame that comes with being branded a cheat is much harder to measure, according to the Proteas' skipper.

"I can understand it's a really tough time for him to be in right now," du Plessis said after the Proteas smashed Australia by 322 runs in the third Test.

"Obviously the situation I was in was really difficult for me as well. Because people were attacking me, my personality and my character.

"And I felt it was wrong. It wasn't fair.

"I don't know how he feels about his own situation.

"Ball shining versus ball tampering, they're two very different situations. One is definitely much more serious than the other."

Du Plessis, generally forthright in his dealings with the media, was relatively diplomatic when asked whether Smith cheated.

"It's difficult for me to answer. What he did is against the ICC rule book. He knows that, he's owned up to it," he said.

"It's not right to do that but he's put his hand up and I suppose now he can try and move forward and the Australian team are going to try and move forward.

"He's trying to take responsibility, so there's right in that."

Du Plessis and Smith are former teammates at Indian Premier League side Rising Pune Supergiant.

It would be a stretch to say they're friends, but Smith noted earlier this month he gets on quite well with du Plessis.

Du Plessis thanked Smith for his support during 'mintgate' in 2016, sending the Australian star a message that noted "he gained a lot of respect from my team".

The South African star, speaking on Sunday, wasn't surprised by how Smith's compatriots back home reacted to the indiscretion.

"When I was in Australia it felt like the same. I was being followed everywhere I went," du Plessis said.

Qantas tour of South Africa

South Africa squad: Faf du Plessis (c), Hashim Amla, Temba Bavuma, Theunis de Bruyn, Dean Elgar, Heinrich Klaasen, Quinton de Kock, Keshav Maharaj, Aiden Markram, Morne Morkel, Chris Morris, Wiaan Mulder, Lungi Ngidi, Duanne Olivier, Vernon Philander, Kagiso Rabada, AB de Villiers.

Australia squad: Steve Smith, David Warner, Cameron Bancroft, Pat Cummins, Peter Handscomb, Josh Hazlewood, Jon Holland, Usman Khawaja, Nathan Lyon, Mitchell Marsh, Shaun Marsh, Tim Paine, Jhye Richardson, Chadd Sayers, Mitchell Starc.

Warm-up match: Australia beat South Africa A by five wickets. Report, highlights

First Test Australia won by 118 runs. Scorecard

Second Test South Africa won by six wickets. Scorecard

Third Test South Africa won by 322 runs. Scorecard

Fourth Test Wanderers, Johannesburg, March 30-April 3. Live coverage