Seven policemen, including an assistant commissioner of police, were injured on Tuesday during the protest by farmers on Delhi-UP border, Delhi Police said here.
Police said a section of crowd suddenly turned violent as police tried to persuade the protesters, who were participating in the Bharatiya Kisan Union march, not to break the barricades.
Police said they used 20 tear gas shells and water cannons to manage the crowd, adding it was "minimum required force".
As many as 3,000 police personnel were deployed to ensure that the farmers are not able to enter Delhi.
The main demands of the agitating farmers include implementation of the recommendations of the Swaminathan Commission report, removing ban on the use of tractors which are more than 10 years old, clearing out pending payments of sugarcane purchase, increased price of sugar supplied and minimum support prices.
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