Believe it or not, Capture the Flag originated on the battlefield of some of the most deadly wars in history. In fact, that was exactly how all the soldiers knew when a battle was over - once the enemy's flag was captured, both sides considered the skirmish settled. In the Civil War, soldiers that were able to either capture the enemy's flag or save their own were rewarded with a Medal of Honor. Nobody knows for sure when Capture the Flag took off as an outdoor activity, but Boy Scouts have been playing the game for over 60 years!
http://www.kidzworld.com/article/4670-your-guide-to-capture-the-flag