The boos that echoed from three-quarters of Leoforos Alexandras Stadium could not blank out the message held up by the small but inescapable minority. As Panathinaikos and the visiting AEK Athens entered the field for Monday’s derby a 40-metre banner was unfurled by the home ultras group, Gate 13, to a backdrop of billowing green and blue smoke. “Free the boys,” it read, and the reaction from all sides left no doubt that its meaning had resonated. While Gate 13’s fellow supporters aired their disgust, the AEK players headed back to the touchline. This was a shocking affront to one...