Verb
(intransitive, originally of sick elephants) To begin to behave in an erratic, uncontrolled, dangerous, destructive, or savage way.
(intransitive, idiomatic) To behave in a very unconventional, independent, uncontrolled, or unauthorized way that ignores rules, norms, or expectations.
(intransitive, idiomatic) To switch allegiance to, affiliation with, or membership in, a country, political party, employer, club, etc. (for example, as a spy, soldier, politician, employee, club member, etc.).
Source: en.wiktionary.org