Fan clubs of two national soccer teams clashed Sunday outside the Estadio Nacional in Sabana Norte. Police detained nearly a dozen.
The rowdy participants were from La Ulta, fans of Deportivo Saprissa, and La 12, supporters of the Liga Deportiva Alajuelense.
The two groups have scuffled before, and stadium rules have changed to keep them separate. But in the electronic age, the taunting can continue online. Both groups of fans have Web pages.
The Fuerza Pública had to knock down some rowdy fans in order to carry them off to detention.
At least two were being sent to the the flagrancy court.
One minor was found with a sharp object, police said.
The scuffles broke out abut 11 a.m. in advance of a soccer match. Such developments are expected when the two soccer rivals meet.
In the past, one group has stoned the bus of their rival. Stadium officials try to keep out the more rowdy fans, many of who are in their 20s and even 30s.