Australia coach Justin Langer slammed the criticism of Steve Smith, labelling it a "load of rubbish".

Smith was questioned after footage showed him standing at the crease and shaping up as if he was batting, including marking a guard, as India survived for a draw on the final day of the third Test in Sydney.

His actions at the crease forced India's Rishabh Pant to retake his own guard before play resumed, with the moment becoming a hot topic on Twitter.

But Langer hit out at the talk about Smith, who was sacked as Australia captain and banned for 12 months following the ball-tampering scandal during the tour of South Africa in 2018.

"I literally cannot believe some of the rubbish I read about Steve Smith, absolute load of rubbish," he told a news conference on Wednesday.

"If anyone knows Steve Smith, he's a bit quirky. We've all laughed about it for the last couple of years and I've spoken about it privately about how he's a bit quirky. What Steve Smith does at the crease, he does it probably most games, he's just thinking about the game.

"Anyone who suggests for one millisecond he was trying to do something untoward, way out of line, absolutely out of line. On that wicket, it was that flat, and it was like concrete, you need 15-inch spikes to make an indent on the crease and he went nowhere near the crease.

"I thought that was absolutely ludicrous and again in the last couple of years since he's been back, he has been exemplary on and off the field, he has let his bat do the talking, he was abused like I've never seen anything through England and he just kept smiling and letting his bat do the talking, give me a break, give me a break."

Australia captain Tim Paine, meanwhile, apologised on Tuesday for his behaviour during the third Test, including sledging Ravichandran Ashwin.

Langer backed Paine and said the 36-year-old would remain captain for the foreseeable future.

"You have no idea how much faith I've got in Tim Paine. He didn't have his best day, no doubt about that, but after three years, he has hardly put a hair out of place, he has been outstanding as the Australian captain, everything he does," he said.

"He had a frustrating day. We've got to cut him some slack surely. But having said that when you set a standard as high as he does and as we do, we understand we're going to get criticised when we fall below that, it's not what we're about.

"But Tim Paine, outstanding leader and will continue to be for some time to come yet. He has my 100 per cent support."

The series is locked at 1-1 ahead of the fourth Test starting in Brisbane on Friday.