BEIJING — It started Wednesday morning as a squabble between an unlicensed watermelon vendor and the widely despised urban management agents who prowl China’s streets looking for scofflaws. Words were exchanged, blows were landed and in the end, the vendor, Deng Zhengjia, 56, lay dead on the pavement in Linwu, a city in central Hunan Province, as angry bystanders photographed his body with their cellphones.

The Linwu police say Mr. Deng “unexpectedly fell to the ground and died.” Witnesses assert that an officer struck Mr. Deng in the head with a weight from his hand-held scale. Hours later, when the police tried to take away his body, a crowd violently fought back, producing images of bloodied faces and generating another wave of outrage.

Mr. Deng’s death has once again drawn national attention to China’s army of urban management officials, known as chengguan, who occupy an awkward and ill-defined place in the government’s apparatus to maintain stability. More powerful than private security guards but lacking the authority to make arrests or carry weapons, chengguan have for many Chinese become the most visible face of the government’s authoritarian impulses.

Responsible for dealing with sanitation complaints, unlicensed construction and illegal peddling, they often seize goods with impunity, beat those who resist and issue what critics describe as arbitrary fines. Between July 2010 and March 2012, the Chinese news media reported 150 cases of abuse by chengguan, according to a recent report by Human Rights Watch.