der Verteidiger
defender
In sports, a player whose main task is to stop attacks by the opposing team and prevent goals.
Der Verteidiger konnte den Stürmer im letzten Moment stoppen.
The defender was able to stop the striker at the last moment.

defender / defense attorney
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defender
In sports, a player whose main task is to stop attacks by the opposing team and prevent goals.
Der Verteidiger konnte den Stürmer im letzten Moment stoppen.
The defender was able to stop the striker at the last moment.

'Der Verteidiger' (the defender / defense attorney) is the noun form of the verb 'verteidigen' (to defend). The ending '-er' indicates the male person who performs this action. Someone who defends is a 'Verteidiger' (defender).
Er verteidigt seine Meinung sehr energisch.
He defends his opinion very vigorously.
The context makes clear which meaning is intended. In a sports context, it refers to a player. In a legal context (in court), it is a lawyer. If it is about ideas or values, it is a person who supports them.
Der Verteidiger verhinderte ein sicheres Tor. (Sport)
The defender prevented a sure goal. (sports)
In sports, 'Verteidiger' (defender) is often combined with positions or qualities. Typical examples are 'Innenverteidiger' (center back), 'Außenverteidiger' (fullback), or 'ein kopfballstarker Verteidiger' (a defender who is strong in the air).
Die Mannschaft hat zwei sehr schnelle Außenverteidiger.
The team has two very fast fullbacks.
In legal contexts, there are specialized terms. You often hear 'Strafverteidiger' (criminal defense attorney) for criminal trials or 'Pflichtverteidiger' (court-appointed defense attorney) for a lawyer appointed by the court.
Da er sich keinen Anwalt leisten konnte, wurde ihm ein Pflichtverteidiger zugewiesen.
Since he could not afford a lawyer, he was assigned a court-appointed defense attorney.
opponent
'der Gegner' and 'der Verteidiger' are often on different sides of a situation. An opponent competes against someone or works against a person, group, or idea. A defender, on the other hand, protects their own side, a person, or a cause from attacks or criticism. In sports, 'der Gegner' is usually the other team, while 'der Verteidiger' is a player who stops attacks. So the contrast is: 'der Gegner' comes from the other side; 'der Verteidiger' protects against that other side.

Der Verteidiger stellte sich vor den Angreifer und stoppte den Ball.
The defender stepped in front of the attacker and stopped the ball.
Der Gegner hat kurz vor dem Ende noch ein Tor geschossen.
The opponent scored another goal shortly before the end.