It's part of a ticket price protest
A German Cup game has had to be halted after fans threw tennis balls onto the pitch as part of a protest against ticket prices.
The incident happened during the match between VFB Stuttgart and Borussia Dortmund.
Liverpool fans staged their own action at the weekend, with thousands of fans departing their Anfield match with Sunderland in the 77th minute over plans for a £77 matchday ticket next season.
Dortmund fans protesting ticket prices tonight by bombarding the pitch with tennis balls. As you do.https://t.co/1qsAsfjumm— Boylesports (@BoyleSports) February 9, 2016