Police in Heidelberg have opened an investigation after a man admitted to generating a high-pitched sound as an "antidote" to rival fans' chants during a Bundesliga match on Saturday.

The man, who was an employee at German club Hoffenheim, used a sound system that emitted a shrill noise during the club's 1-0 home game against Borussia Dortmund.

It is believed the employee had been trying drown out what he thought were unbearable insults aimed at Hoffenheim's major investor, billionaire Dietmar Hopp.

The wooden device, which didn't disrupt play, was placed near the Dortmund fan section behind a goal at the Rhein-Neckar Stadium.

Police initiated the investigation after a Dortmund fan pressed assault charges. The fan from Pforzheim was diagnosed with tinnitus and was forced to miss work.

'Supposed to be humorous'

Hoffenheim issued a statement on Tuesday apologizing for the incident, which they said had occurred without the knowledge of management.

The employee was "unaware of the seriousness of his action which was meant to be humorous," the statement said.

"Neither the club nor the president nor Mr. Hopp were aware of the equipment's existence," it added. "We distance ourselves from the action and apologize to all football fans if their experience was affected."

Heidelberg police have asked for the homemade apparatus to be delivered to them for investigation.

Author: Charlotte Chelsom-Pill (Reuters, dpa)

Editor: Martin Kuebler