The race to lead São Paulo, Latin America’s largest city, has been transformed in recent weeks by the brash candidacy of a right-wing self-help coach who has soared in the polls while getting under his opponents’ skin with harsh and sometimes misleading attacks.

In a live, televised mayoral debate between six candidates on Sunday, that candidate, Pablo Marçal, was at it again, calling José Luiz Datena, an anti-crime television journalist, a vulgar insult and bringing up sexual harassment accusations against him that were later dropped.

“You crossed the debate stage recently to slap me,” Mr. Marçal said, referring to an earlier debate, in which Mr. Datena got close to Mr. Marçal. “You’re not even man enough to do that.”

He then looked to his right and, from offscreen, Mr. Datena came swinging an iron chair, striking Mr. Marçal over his back.

It was a stunning moment even for the often outrageous political antics of Brazil — one candidate assaulting another on live television — and a show of political violence that was likely to reorder the country’s biggest election this year.

Mr. Marçal quickly capitalized, posting multiple videos on social media after the attack, including a dramatized clip of him being rushed to the hospital and breathing with the help of an oxygen mask. He also posted from the hospital, clad in a hospital gown with an arm sling.