Normally this occurs when commitments have been made for construction of buildings, hiring of faculty, and the like. Pledges are legally enforceable commitments and the courts have sided with campuses in the past. Obviously, this is an extreme situation and, fortunately, not one that occurs frequently in my experience. What normally happens, short of going to court, is that institutions work with donors' families to find a solution that meets everyone's needs. The financial aid decision is based on a number of factors and only a qualified financial aid counselor on a campus can help you with this one.
Sports are hugely controversial on the nation's campuses.
Many athletes don't graduate, and don't try to. Many schools cave in to winning coaches who bring them money, even if those coaches behave like children. A school that does it the right way can still win. I was personally rooting for Stanford to win it all this year, which is also a great program. I think in order for more schools to be like them, academic achievement needs to be placed first over athletics.