The ultra groups of Spain's premier division teams have their own names. Athletic Bilbao's hardcore fans are called Herri Norte Taldea (HNT); Real Madrid's are known as the Ultras Sur. Neither group likes the other.
There's a song that HNT sing whenever Athletic play Real Madrid (a melody to the tune of "When the Saints Go Marchin' In"): "We don't like violence in football grounds/We don't like violence in San Mames/We have to kill, we have to kill/We have to kill an Ultra Sur/We have to kill an Ultra Sur/We have to kill an Ultra Sur.