Scuffles broke out outside a court in China where a blind activist who raised concerns about forced abortion and sterilisation was due to be tried.
Chen Guangcheng had accused officials in Linyi city, Shandong province, of breaking family planning laws in their enforcement of the one-child policy.
He has been under house arrest since September 2005, and is charged with public order offences.
Thursday's trial was postponed at the prosecution's request, his lawyer said.
Activists and supporters had gathered outside the court in Shandong to support Mr Chen, whose case has attracted considerable attention.
One man told the French agency AFP that he and 10 other activists who had travelled from Beijing were detained after scuffles with men they described as plain-clothes policemen.
Mr Chen had alleged - via the US media - that health workers in Linyi city were forcing people to have abortions or sterilisations.
An article in Time magazine in September 2005 claimed that some 7,000 people had been sterilised against their will in Shandong province.
Several workers were later arrested or sacked over the claims, state media reported, acknowledging "successive complaints" about illegal practices in Linyi.
China brought in its one-child policy 25 years ago, in a drive to curb population growth. Urban couples are offered strong incentives to have no more than one child, while policy is rural areas is more relaxed.
However, the government does not authorise health workers to carry out forced sterilisation and abortions.
Mr Chen faces charges of "wilfully harming public property" and "gathering masses to disturb traffic order".
A new date for his trial, which has already been delayed once, has not yet been set.