The instructions were concise and clear. Those hoping to march to the stadium with Hungary’s fans for their soccer team’s first game of the European Championship were expected to report by 10 a.m. sharp, five hours before kickoff. A strict dress code would apply. Some could wear black. Others were to stick with red, white and green, the colors of the country’s flag. Under no circumstances was there to be any flashiness. “Gaudy colors, clown hats and bagpipes” were all prohibited. They were, prospective marchers were reminded, “going to a soccer stadium, not a circus.” The hectoring and slightly priggish...