In my experience, the biggest difference in the stadium experience of domestic European football and American sports is the lack of the wave. The wave is safe. It is basically an exercise in following directions, a mechanism that forces everyone to play nice. Contrast this with a European crowd: flares, smoke, projectiles, police who don’t fistbump the players but stare intently at the crowd with their backs to the field, a subtle undercurrent of racism all fueled by 1 liter beers (only 3%, though). One is more corporate sponsor friendly, the other more exhilarating since you’re never sure just what might happen.