Here is a pretty good explanation from Wikipedia:

In the National Collegiate Athletic Association (NCAA), a show-cause penalty is an administrative punishment ordering that any NCAA penalties imposed on a coach found to have committed major rules violations will stay in effect against that coach for a specified period of time—and could also be transferred to any other NCAA-member school that hires the coach while the sanctions are still in effect. Both the school and coach are required to send letters to the NCAA agreeing to abide by any restrictions imposed. They must also report back to the NCAA every six months until either the end of the coach's employment or the show-cause penalty (whichever comes first). If the school wishes to avoid the NCAA penalties imposed on that coach, the college must send representatives to appear before the NCAA's Committee on Infractions, and "show cause" (i.e., prove the existence of good reason) as to why it should not be penalized for hiring that coach.[1] The penalty is intended to prevent a coach from escaping violations that he/she had a role in committing or allowing—which are generally applied to the school (e.g., lost scholarships, forfeited wins) -- by merely resigning and taking a coaching job at another, un-penalized school. It is currently the most severe penalty that can be brought against an American collegiate coach.

Contrary to popular belief, an NCAA member school is allowed to hire a coach who is under an ongoing show-cause order. However, the show-cause restrictions make it prohibitively difficult for a coach with a show-cause order to get another collegiate job. As mentioned above, any school that hires a coach with an outstanding show-cause order can be penalized merely for hiring him. Additionally, that school could be severely punished if such a coach commits additional violations while the show-cause order is still in effect.[2] Consequently, most schools will not even consider hiring a coach with a show-cause penalty in effect, meaning that it usually has the effect of blackballing that coach from the collegiate ranks for the duration of the penalty. Many coaches who receive a show-cause penalty never coach again, even after the penalty expires, since a large number of athletic directors and university presidents are unwilling to hire someone with a history of major violations.[3]