Shares of Zillow Group (Z -13.49%) (ZG -13.02%) fell 13.5% on Friday after the National Association of Realtors (NAR) agreed to settle a series of lawsuits brought by home sellers alleging the industry has conspired to boost agent commissions.The move appears likely to pave the way for reduced broker commissions on real estate sales -- a development that could potentially curb one of Zillow's bread-and-butter revenue streams.On the NAR's historic settlementIn a press release earlier today, the NAR announced ...