The conservative party, headed by Christoph Blocher, saw several of its members physically attacked by the anti-free speech protestors, while waiting for the police to arrive. Several stands at the planned rendez-vous point were overturned before being set on fire... while the UDC members were still within them.
An account from Yahoo France [my translation]:
Violence erupted Saturday afternoon in Berne, leaving at least 20 wounded, of which 17 were police officers, according to local authorities. Hundreds of extreme left protestors destroyed the equipment installed in front of the Parliament for an electoral meeting of the nationalist UDC party, and played havoc until the police dispersed them with tear-gas.
In the early part of the afternoon, some 10,000 of sympathizers of the [UDC] had assembled in Berne for a parade in the streets of the old city up to Federal Place, where a large party had been planned, 15 days before the oct 21 federal elections. Yet several hundred counter-protestors dressed in black prevented them from attaining their rendez-vous. Sympathizers of the “Black Block” then moved over to Federal Place. The installations there were destroyed.
Restaurants were damaged, windows of banks were broken and cars set on fire. According to witnesses, several people were wounded. Several dozen members of the "Black Block" [group] were arrested, according to municipal police spokesperson Thomas Jauch.
UPDATE: For some reason I was difficulty posting video today. Below is a german-language news account of the violent extreme left rioters trashing the UDC rally in Berne.