NEW YORK CITY - A Sikh professor at Columbia University who had written about hate crimes against the community said late Monday he became a victim himself during a group attack in New York.Prabhjot Singh, an assistant professor at the Ivy League university’s School of International and Public Affairs, said he was assaulted Saturday evening after dropping off his wife and one-year-old son. Around 20 teenagers, some on bicycles, shouted “Get Him!” and “Osama!” at Singh, who as an observant Sikh maintains a beard and turban, he said.Singh said that he was repeatedly punched and his beard was pulled during the attack just north of Central Park in Harlem. He spent a day undergoing surgery for displaced teeth and other wounds. Singh, 31, who conducts community health projects in Harlem, said the attack made him “ever more committed to our community.” “It’s not the Harlem I know and it’s certainly not going to change how I move about the neighbourhood,” he told a news conference.Asked what he would say to his assailants if he encountered them, Singh said he would invite them to a Sikh temple, known as a gurdwara. “I would ask them if they had any questions, if they knew what they were doing,” he said.“I think that the bottom line is when you’re 14 or 15, you pick up messages all across the community,” he said, calling for efforts to counter factors that “gave these kids the green light of hate.”Sikhs have faced a wave of violence in the United States following the September 11, 2001 attacks, sometimes by assailants who mistakenly believe they are radical Muslims.Sikhism, founded in South Asia five centuries ago, requires men to maintain beards and turbans.In the deadliest attack, white supremacist US Army veteran Wade Michael Page shot dead six Sikh men at their temple in Wisconsin in August 2012.After that attack, Singh co-authored an opinion piece in The New York Times that encouraged the US government to document anti-Sikh violence.“Whatever the roots of Mr. Page’s hatred, it is wrong to assume that every attack against a Sikh is really meant for a Muslim,” it said, pointing to the “long history of discrimination and hatred directed at Sikhs in America.”The Federal Bureau of Investigation announced last month that it would start documenting hate crimes against Sikhs and several other groups. It already compiled statistics on anti-Muslim attacks.The latest attack came days before Indian Prime Minister Manmohan Singh, a Sikh, visits Washington and the United Nations in New York.