Out of all of the possible rules violations cited by the NCAA in their letter to Penn State the following one really stands out:
"Lastly, it is important to bring to your attention that Bylawy19.01.2 affirmatively states that "individuals employed by, or associated with member institutions for the administration, the conduct or the coaching of intercollegiate athletics are, in the final analysis, teachers of young people. Their responsibility is an affirmative one, and they must do more than avoid improper conduct or questionable acts. Their own moral values must be so certain and positive that those younger and more pliable will be influenced by a fine example."
"This provision has been cited by enforcement in at least half a dozen major infractions cases in the past. This provision has been cited by enforcement in at least half a dozen major infractions cases in the past. Those who exhibit this behavior are meeting the ethical expectations of NCAA membership. Those who do not, fail us all."
http://www.psu.edu/ur/2011/NCAA.pdf