The promotion of RB Leipzig to the Bundesliga has caused resentment among hardcore fans of traditional teams, sparking fears that 'plastic clubs' could ruin the traditional culture in Germany's top flight.

RB Leipzig is backed by Austrian energy drink giant Red Bull, which took over a soccer license and founded the club in 2009.

The team was renamed RasenBallsport Leipzig, specifically to get around the German league rule forbidding teams from carrying a sponsor's name.

Four promotions in seven years has taken Leipzig to the Bundesliga, and its young squad is unbeaten after six games in their first season in the top tier.

The team has beaten both Borussia Dortmund and Hamburg and drawn with powerhouse clubs Cologne and Borussia Moenchengladbach.

But its impressive performances so far in the debut season has earned little respect from Germany's hardcore fans - known as 'Ultras'.

Some Leipzig matches have been boycotted and a severed bull's head was even thrown onto the playing area for an away German Cup match.

Ultra fans of Cologne blocked the Leipzig team bus for a home game in September, which led to the kickoff being delayed, while banners reading "We Hate RB" were on display around the city.

Borussia Dortmund's Ultras boycotted the club's away game in Leipzig last month, with support groups refusing to put their money into Red Bull's pockets.

'Basic difference'

"Red Bull Leipzig is leading the whole system of football to ad absurdum," filmmaker and Dortmund fan Jan-Henrik Gruszecki told broadcaster Sport 1.

"Traditional clubs like Dortmund, Schalke, Cologne and Bayern Munich want to make money and play football.

"Red Bull wants to sell a product and a brand. This is the basic difference."

Hostility towards sponsored teams in Germany's top flight is nothing new, but RB Leipzig has crystalized growing resentments.

Ingolstadt, Bayer Leverkusen, Wolfsburg, Hoffenheim and now Leipzig are all backed by wealthy companies or individuals.

None are widely popular and all are dubbed 'plastic clubs.'

Last season, when Wolfsburg, backed by car manufacturers Volkswagen, played Bayer Leverkusen, sponsored by pharmaceutical firm Bayer, trade magazine Kicker dubbed it 'El Plastico', a play on words using the 'El Clasico' reference to the Real Madrid-Barcelona clash.

Theoretically, Germany has a rule that is aimed at preventing outright ownership of clubs by individuals or institutions.

The 50+1 rule also states a club must hold a majority of its own voting rights.

But Leipzig bypassed the 50+1 rule with 51 percent of the club owned by Red Bull employees - with the other 49 percent owned by Red Bull.

"The peculiarity of the culture of football in Germany is that the clubs were founded as an association, in which the supporters have control of power and decision-making," said Jonas Gabler, an expert on soccer culture in Germany.

"The wishes and interests of the fans are taken very seriously.

"This interaction of fans with their clubs is an essential element of the culture of football.

"Now fans have the impression that this tradition is perverted by clubs that are created by companies."

Fans of traditional teams criticize plastic clubs for relying on a sponsor, who can withdraw the cash at will, and for taking the place in the top flight of a less wealthy club.

For example, Leipzig beat Nuremberg, which has a strong tradition in Germany's top flight, to an automatic promotion spot last season.

Reasonable ticket prices are a feature of German club soccer but fans fear a deterioration of the mutual respect between clubs and their supporters could lead to a rise in prices.

"Many leaders personally reject this economic model, and many prefer not to oppose the majority of fans on this, so they remain cautious," said Gabler.