(Reuters) - Total net revenue at William Hill plunged 57% in the weeks following the start of coronavirus lockdowns in Europe and North America, as sports betting volumes collapsed and it was forced to close its retail network of betting shops.In a trading update on Friday, the British bookmaker also pulled all future forecasts as it reported online betting revenue fell 21% in the seven weeks to April 28.The firm expects each additional month of shop closures to impact core earnings by up to 15..