Australia head coach Justin Langer has come to the defence of Tim Paine and Steve Smith after the pair were criticised for their actions in the third Test against India.

Captain Paine was fined 15 per cent of his match fee for showing dissent to an umpire earlier in the Test and was part of a heated verbal exchange with India's Ravichandran Ashwin during play in Sydney.

And Smith was caught by the stump camera scratching at the crease line with his boot during Rishabh Pant's innings, although his intention has been the subject of much discussion.

Langer, speaking at a virtual press conference on Wednesday, said his captain had "100 per cent support".

He added: "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 are about.

"Tim Paine ... outstanding leader and will continue to be for some time to come yet.

"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 in everything he does. He had a frustrating day."

Australia were in the driving seat going into the final day of the Test, but India stood firm to secure a memorable draw.

On Smith, Langer said anyone who suggested the batsman was doing anything untoward was "absolutely out of line".

He added: "That wicket was that flat and it was like concrete, you would need 15 inch spikes to make an indent on the crease, and he went nowhere near the crease.

"If anyone who knows Steve Smith ... he's a bit quirky and he does some weird (things) and we've all laughed about it.

"It's what Steve Smith does at the crease. He does it probably at most games, he's just thinking about the game."