intervene

verb6

1. •
   To become involved in a situation, so as to alter or prevent an action.

   • The police had to be called to intervene in the fight.
2. •
   To say (something) in the middle of a conversation or discussion between other people, or to respond to a situation involving other people.

   • Young Scarfe stared, astounded. “You haven’t met before,” Mrs. Gould intervened. “Mr. Decoud—Mr. Scarfe.” — 1904
3. •
   In a suit to which one has not been made a party, to put forward a defense of one's interest in the subject matter.

   • an application for leave (i.e. permission) to intervene
4. •
   To occur, fall, or come between, points of time, or events.

   • An instant intervened between the flash and the report.
5. •
   To come between, or to be between, persons or things.

   • The Mediterranean intervenes between Europe and Africa.
6. •
   To occur or act as an obstacle or delay.

   • Nothing intervened to prevent the undertaking.
   • The weather intervened before the contest could get under way.