Dortmund fans protest ticket prices with tennis balls

It's been a week of protesting rising soccer tickets costs, and Borussia Dortmund fans used the German Cup match against Stuttgart to show their frustration.

The fans are angry at being charged €19.50 ($22) for standing tickets and €38.50 ($43) for the cheapest seats - which, if you compare to the £77 ($111) Liverpool fans were griping about, this seems like a steal.

It was a multi-pronged approach, starting with a banner in front of empty seats reading: "Football must be affordable."

The fans boycotted the first 20 minutes of the match and made a bit of a scene walking in.

And then, last but not least, the fans threw tennis balls onto the field.

No, we don't really get the symbolism of the tennis balls either -- and making the players clean up the mess? Not cool.