Like many sports fans across the world, Dortmund fans are upset with increasing ticket prices at sporting events. Unlike many sports fans, they decided to voice their displeasure by pelting tennis balls on the field in the middle of the team's match against VfB Stuttgart.
According to The 42, Dortmund supporters have to pay €19.50 ($22.02 USD) for standing tickets and €38.50 ($43.48 USD) for the cheapest seats. Visiting fans are paying as much as €70 ($79.05 USD).
Dortmund led the German football Bundesliga in attendance last season with an average of 80,463 attendees per match.