Legal experts said that public anger had probably influenced the ruling.

“The court considered China’s family values and the idea of respect for the mother,” said Cao Shuchang, a partner at King & Capital, a law firm in Beijing. “For a mother to be hurt in that way, under those circumstances, it would be inhumane for a man not to act.”

Fu Hualing, a law professor at the University of Hong Kong, said the case had posed a predicament. On the one hand, officials may have been eager to show some sympathy for the harsh circumstances the defendant had faced. On the other, Professor Fu said, the government most likely wanted to signal that it would not tolerate violent acts.

“The state doesn’t want society to use violence on its own, regardless of how legitimate it might be,” Professor Fu said. “The state wants to monopolize the use of violence, to tell people, ‘Come to us, we will help you out, but don’t do it on your own.’ ”

The case shed light on the illicit world of loan sharks in China. Many have resorted to thuggish tactics in recent years, as defaults have increased and as it has become more difficult to collect debts. Several of the men who harassed Ms. Su were later arrested on suspicion of having ties to organized crime.

Small-business owners, fearing retribution, are often powerless in the face of harassment. Ms. Su was paying an interest rate equivalent to 120 percent a year on a loan related to her car parts business, far exceeding the national limit of 36 percent, according to court records.

The episode also raised questions about the willingness of the police to fight on behalf of ordinary citizens.

Chinese news reports suggested that Mr. Yu had lashed out at least in part because police officers had left the scene without resolving the situation. A court later exonerated the officers. On Friday, China Central Television, the state broadcaster, showed a video of the officers urging the men not to fight.