An attacker is someone who initiates violence or hostility against another person or group. In sports like soccer or hockey, attackers are players whose main job is to move toward the opponent's goal and try to score. In military contexts, attacking forces are those launching an offensive operation rather than defending their position.

The word carries different weight depending on the situation. In a schoolyard conflict, an attacker might be someone who starts a fight or bullies another student. In cybersecurity, an attacker is someone trying to break into computer systems to steal information or cause damage. In chess, you might describe aggressive play as an “attacking style,” moving your pieces forward to threaten your opponent's king.

Notice that attacker implies taking the initiative rather than responding. If someone defends themselves after being hit, they're not the attacker. In soccer, when a team loses possession and switches from attacking to defending, attackers must quickly fall back to help protect their own goal. The word describes both the role someone plays and, in serious contexts, someone whose actions cross important lines of safety and respect.