As the game unfolded the crowd around us roared and cheered, leaping to their feet each time a player succeeded in bouncing the ball past the center line and groaning whenever an end-zone player threw his body in front of the ball to block a point. The spectators seemed evenly divided between local Jaguar fans and supporters of the Texcoco Serpents. And tensions were running high. Three rows below us, a fight broke out between two rival fans. I winced as ACS guards in tan uniforms waded in, using stun batons to zap the unruly fans into submission. One of the men collapsed under the baton’s sting—there was no way to tell whether he’d had a heart attack or had simply fainted. The security guards dragged him away, disappearing with him down one of the corridors that led to the concourse of the tlachtli . The other combatant looked shaken, and meekly sat down again.