The headquarters of Argentine first division club Newell's Old Boys was attacked by an armed gang who vandalised property and intimidated staff, police and club officials told local media on Monday.
The gang, numbering around 30 and armed with guns and baseball bats, were believed to belong to a faction of the Rosario-based club's own supporters, officials added. Twenty-one people were arrested.
Newell's treasurer Jorge Ricobelli told local media that the gang burst into administrative officers at the club's Parque Independencia stadium where new members were enrolling.
They then moved on to the barbecue area and a covered gymnasium, forcing members to leave, vandalising property and firing shots at a tree and a water tank, reports said.
Rosario police official Miguel Angel Rodriguez told reporters that the gang was linked to the club's own fans.
Newell's, one of the country's most popular provincial clubs, have recently undergone a tumultuous leadership change, with the controversial, long-serving president Eduardo Lopez defeated in last month's elections by a new group led by Guillermo Llorente.
Argentine soccer suffers from chronic soccer hooliganism blamed largely on groups of hardcore fans known as barras bravas.
Many groups are split into factions who sometimes fight among themselves and often take sides in internal political disputes between directors.