The Bundesliga match between Bochum and Borussia Moenchengladbach was abandoned after the assistant referee was struck on the head by a beer cup thrown from the stands.
Gladbach had been leading 2-0 at Bochum following second-half goals from Alassane Plea and Breel Embolo when the match was interrupted after 71 minutes when linesman Christian Gittelmann took a blow to the head.
The referee took the decision to stop the game for good after 20 minutes.
Both clubs immediately took to social media to condemn the incident.
“We can only formally apologise to linesman Christian Gittelmann,” Bochum said on social media.
“A highly embarrassing and bitter evening for us. An extremely stupid action from an idiotic fan.”
Gladbach sporting director Roland Virkus added: “Things like this should never happen. It angers you when a good game of football has to end like this.”
Bochum had been 11th in the table, two points ahead of Gladbach, in 13th position, before the game.