When might a Sprint be abnormally cancelled?

According to the Scrum Guide1, a Sprint can be cancelled before the Sprint time-box is over. Only the

Product Owner has the authority to cancel the Sprint, although he or she may do so under influence

from the stakeholders, the Developers, or the Scrum Master. A Sprint would be cancelled if the Sprint

Goal becomes obsolete. This might occur if the company changes direction or if market or

technology conditions change. In general, a Sprint should be cancelled if it no longer makes sense

given the circumstances. But, due to the short duration of Sprints, cancellation rarely makes sense.

Reference: Scrum Guide