In current usage, any disastrous situation. The balls referred to are NOT testicles. The term dates from the days of wooden sailing ships when the existence of a shipboard disaster, such as plague, lack of food or water, mutiny, etc. was communicated to the outside world by hoisting large, brightly painted wooden balls up into the rigging. Balls of different colors represented different disasters and therefore served as either requests for assistance or warnings to stay clear.