India batsman Virat Kohli was fined half of his match fee on Thursday for responding to barracking from the crowd by gesturing at them with his middle finger on day two of the second Test against Australia.

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India spent all day in the field at the Sydney Cricket Ground on Wednesday, taking just one wicket as the Australian batsmen ran rampant and put themselves in a good position to go 2-0 up in the series.

Kohli, fielding at the boundary for much of the day, tweeted that he had been sorely provoked before responding with the finger gesture.

"I agree cricketers dont have to retaliate. What when the crowd says the worst things about your mother and sister. The worst I've heard," he posted on his twitter page (twitter.com/imvkohli).

India team spokesman GS Walia told reporters on Thursday that match referee Ranjan Madugalle had fined Kohli 50 percent of his match fee for the offense.

The player had pleaded guilty and was sorry for his action, Walia added.

The four-match series has so far been played largely in a good spirit, in stark contrast with the 2008 Sydney Test which was marred by accusations that India spinner Harbhajan Singh had racially abused Australia's Andrew Symonds.