A trolley bus carrying revelers during the Seattle Sounders' championship parade Tuesday struck and injured a policeman, according to the Associated Press.
One of the four trolleys involved the procession collided with the bicycle officer as it took a turn on a downtown Seattle street.
Thousands of supporters clamoured to celebrate the winners of the 2016 MLS Cup after a tense shootout victory over Toronto FC.
Other police officers strode beside some of the buses, and arrested two people who attempted to climb onto the trolleys.