expression, godan verb (-ru)
turn against; become an enemy
Describes a person or group who was previously neutral or friendly becoming hostile. Often used when someone switches sides or becomes an opponent.
See also: 敵に回す (てきにまわす)
彼を怒らせると、味方だった人も敵に回るかもしれない。
If you make him angry, even someone who was an ally might turn against you.
その発言で、多くの同僚が敵に回った。
With that remark, many colleagues turned against him.