“We are dismayed, shocked and struck by the level of violence, rudeness and attacks against our referees in the amateur game,” the federation wrote in an open letter of support to referees which it said it sent to all its 24,544 clubs.

The DFB's cry of alarm comes after the referee in charge of a local Frankfurt game on Sunday was knocked unconscious by a player he had just sent off.

The official was helicoptered to hospital, where he remains three days later.

This attack followed a weekend strike this month by referees in Berlin in charge of amateur games in protest at the problem.

The DFB said that 80,000 matches are played under its auspices each week and that all 80,000 have referees.

“The formula is simple: no football without referees,” said the letter.

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One club in the German capital, Friedenauer TSC, took the unusual step Wednesday of announcing it would be hiring a bodyguard to ensure the safety of referees at their games.

“The increase in violence, in particular against figures in authority, is a problem that touches all of society,” the DFB wrote in its letter.

“That in no way means that we turn our backs and leave the responsibility to politicians.”

The federation appealed to police and prosecutors to be more diligent when investigating these attacks.

“Football pitches are not no-go zones, attacks on referees are crimes…and so must be treated under the penal code,” the DFB said.