Ahead of last month's match with Eintracht Frankfurt, Dortmund launched a scheme which rewarded supporters for not using their smartphones during games at their 82,000-capacity Westfalenstadion.
By switching on 'fan mode' in the Dortmund app, supporters who kept off their phones were awarded points and could win prizes, including signed jerseys and fan shop vouchers.
But while the scheme likely seems odd, particularly for international fans, it…