A Free State youth died on Tuesday a day after being hit by a police rubber shot during a protest against local authorities and poverty, police said.
Police said some young residents protested again on Tuesday but dispersed when officers fired a stun grenade at them.
The 17-year-old boy who died was among 4 500 young people who took to the streets near their the township of Intabazwe on Monday, briefly halting traffic on the main Johannesburg-Durban highway where they clashed with police.
"At this stage we suspect he was hit by the rubber bullets in the chest," a police spokesperson said, adding a post mortem was planned. South African police fire cartridges of rubber pellets from shotguns to quell riots.
About 20 young people were injured by the pellets on Monday. Most had been discharged from hospital by Tuesday, the spokesperson said.
Police arrested 44 youths on Monday when they blocked the highway and set tyres alight in the township. Most appeared in court later that day charged with public violence and were released on bail.
Around 400 young people gathered again on Tuesday and confronted police at Intabazwe, near Harrismith, leading to 38 more arrests, the spokesperson said.
Their grievances over the poor state of public services were directed at the local mayor and councillors, although they were also protesting against widespread poverty.
A decade after the end of apartheid, many of South Africa's black majority still live in poor townships with few prospects.
The ruling African National Congress was re-elected by a landslide in April on a platform of improving services and bettering the lives of South Africans on the wrong end of one of the world's greatest wealth disparities.
Thousands of residents of a slum settlement near the main business centre Johannesburg rioted for three days in July over reports that some of them were to be relocated, prompting clashes with police reminiscent of years of apartheid violence.