(informal)deserting or revolting against one's group, duties, expected conduct, or the like, especially to establish or join a rival group, change one's life drastically, etc.
“The police bulletin described the runaway chicken as a white leghorn, wearing a flea collar with a silver tag attached.”
“Such a mix of policies would normally lead to runaway inflation.”
“The evidence seems to me to preponderate very largely in favor of the fact that the immediate force which caused the injury to this woman was the runaway horse.”