A few years back, I was listening to a national radio show, with Dennis Green being interviewed. The topic was rivalries. Dennis Green was involved in a lot of rivalries. He was Head Coach of Stanford (rivals with Cal and Notre Dame) and Head Coach of the Vikings (rivals with Green Bay, and the Chicago Bears).
He said the best and most intense rivalry he was ever involved in was the old John Harris/William Penn rivalry.
The old timers on this forum that live or are from the Harrisburg area may remember that the Harrisburg School District had 2 high schools, John Harris High School, and William Penn High School. The 2 schools were HEATED rivals, right up to the time William Penn was closed in the early 1970's.
I was impressed the Dennis Green named this rivalry as being even greater than some of the more famous national rivalries, and did so on a nationally broadcast show.