loose cannon

Noun

 * 1)  A cannon that breaks loose from its moorings on a ship during battle or storm, which has the potential to cause serious damage to the ship and her crew.
 * 2)  An uncontrolled or unpredictable person who causes damage to their own team, faction, political party, etc.
 * Jack is considered a loose cannon due to his volatile personality and his track record of being unable to maintain his composure.

Translations

 * Chinese:
 * Mandarin: 脱缰野马
 * Czech: neřízená střela
 * Dutch: ongeleid projectiel
 * Estonian: ennustamatu käitumisega inimene
 * Finnish: kävelevä katastrofi, arvaamaton ihminen
 * French:
 * German: unberechenbarer Mensch, unkontrollierbarer Mensch, gemeingefährlicher Mensch
 * Hungarian: elszabadult hajóágyú
 * Italian: mina vagante
 * Japanese:
 * Macedonian:
 * Portuguese:
 * Russian: /lit: monkey with a grenade/
 * Spanish: bala perdida
 * Turkish:

Verb

 * 1)  To behave in a way such as to cause damage to one's own faction, political party, etc.