Borussia Dortmund fans have once again protested against high ticket prices, this time throwing tennis balls onto the pitch to interrupt their side's cup game against Stuttgart on Tuesday.
Visiting Dortmund supporters boycotted the first 20 minutes of the DFB-Pokal tie at the Mercedes-Benz Arena, where they were upset at having to pay upwards of €19.50 (£15.19) a ticket.
The purpose of the tennis balls is understood to represent the perception that football fans do not have as much money as tennis followers, with the Dortmund fans wanting to show that they will not be held to ransom over ticket prices and allow the sport to become elitist.
Stuttgart defended the price of the tickets by saying that they were exactly the same as for their Bundesliga fixture with Dortmund, and unchanged since 2012/13.
Dortmund went on to win the game 3-1 and book their place in the semi-finals of the cup.
Dortmund's 'Yellow Wall' of fans staged a similar protest to ticket pricing in 2012 during an away clash with Hamburg, whose cheapest seats were priced at €40 (£31).
Jurgen Klopp, who managed Dortmund at the time, recently said he understood the decision of Liverpool fans to walk out at Anfield over new ticket prices, having experienced similar situations at his former club.
In October last year, Dortmund also sent a reduced ticket allocation to Schalke after their rivals' fans threatened to boycott a match at Westfalenstadion.