The 12th largest US merchant acquirer, Shift4, operates in several verticals but dominates in providing card payment acceptance in sports and entertainment venues. The company processes card payments for all five major sports (baseball, football, basketball, hockey and soccer) in the US using POS terminals, kiosks, mobile wallets and QR codes. More than 50% of the top sporting arenas in the US use Shift4 to process card payments. Amazon, which launched what it calls Just Walk Out checkout  technology in 2018 to support cashier-less retail stores, has installed the autonomous retailing serv...