What is the origin of the idiom 'hang in there'?

Answer 1

Pitchers prefer batters to stand at an increased distance from the plate because this makes it easier to get them out with an outside pitch. In order to persuade the batter to stand further from the plate, pitchers will throw one or more pitchers very close to the batter's body hoping that the instinctive fear of being hit by a pitch will cause the batter to stand further from the plate on the next pitch. When the batter's teammates see this happening, they will shout encouragement to the batter telling him to "hang in there". In other words, don't move away from the plate and thereby give an advantage to the pitcher.

Also nautical: Relief is coming soon.