Pueblo
Pueblo is home to the oldest high school rivalry this side of the Mississippi. It's called the Bell game and is played between Central High School (the wildcats) and Centennial High School (the bull dogs). It is a game that half of the city is very invested in.
The feud between the Hatfields and the McCoys has got nothing on the feud between Central and Centennial, they fight like cats and dogs; "it's a Pueblo thing."