Bosnian cup match halted after linesman hit
A charged atmosphere rife with nationalist chants boiled over midway through the second half when Borac fans hurled a hard object that hit the linesman, forcing referee Midhat Arnatuvic to stop the match.
It was the second successive match between the two teams to be abandoned after their league fixture last September was halted at the same venue when Borac fans invaded the pitch and hurled rocks and flares at Zeljeznicar supporters.
Zeljeznicar were leading 1-0 through a superb Zajko Zeba free-kick on Wednesday when trouble erupted.
Bosnian football has been plagued with violence in recent years as rival fans in the ethnically divided country clash regularly when their teams play each other.
During last September's league match between Borac and Zeljeznicar, the home fans produced a banner hailing Bosnian Serb genocide suspect Ratko Mladic.
In October, a friendly between Zeljeznicar and Croatian side Hajduk Split was cancelled before kick-off in Sarajevo after rival fans turned the streets of Bosnia's capital into a battlefield, injuring dozens of people and damaging cars.
Fighting erupted inside the Grbavica stadium and continued after police drove out the hooligans.