to not be actively involved in something.

The majority of western countries decided to stay on the sidelines during the crisis in the Middle East.

• in the bosom of something
• in the buff
• in the business of
• in the business of doing something
• in the can
• in the cards
• in the catbird seat
• in the clear
• in the closet
• in the cold light of day
• in the cross hairs
• in the dead of night
• in the dead of the night
• in the dead of winter
• in the doghouse
• in the doldrums
• in the driver's seat
• in the dumps
• in the end
• in the event of
• in the event of something
• in the eyes of
• in the eyes of someone
• in the eyes of the law
• in the face of