verteidigen
to defend
To protect someone or something from an attack, danger, or criticism.
Die Soldaten verteidigten die Stadt gegen die Angreifer.
The soldiers defended the city against the attackers.

to defend
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to defend
To protect someone or something from an attack, danger, or criticism.
Die Soldaten verteidigten die Stadt gegen die Angreifer.
The soldiers defended the city against the attackers.

'Verteidigen' (to defend) is an inseparable verb. The prefix 'ver-' remains firmly attached to the verb 'teidigen' in all tenses and sentence constructions.
Er verteidigt seine Meinung mit starken Argumenten.
He defends his opinion with strong arguments.
'Verteidigen' (to defend) is very often used with the preposition 'gegen' (against) and the accusative to name the attack or danger. The pattern is: jemanden/etwas gegen jemanden/etwas verteidigen (to defend someone/something against someone/something).
Der Anwalt verteidigt seinen Mandanten gegen schwere Vorwürfe.
The lawyer defends his client against serious accusations.
When you defend yourself, the verb is used reflexively: 'sich verteidigen' (to defend oneself). When you protect another person or a thing, it is used without 'sich' (oneself).
Das Kind verteidigte seinen kleinen Bruder auf dem Schulhof.
The child defended his little brother in the schoolyard.
The object of the verb reveals the exact meaning: a title is defended in sports, a thesis in academia, an accused person in court, and a city in war.
Der Boxer will seinen Weltmeistertitel verteidigen.
The boxer wants to defend his world championship title.
In the meaning of 'rechtfertigen' (to justify), 'verteidigen' (to defend) is often combined with abstract nouns. Typical phrases are: eine Meinung verteidigen (to defend an opinion), eine Position verteidigen (to defend a position), eine Entscheidung verteidigen (to defend a decision), or eine Ehre verteidigen (to defend an honor).
Er verteidigte seine umstrittene Position bis zum Schluss.
He defended his controversial position until the end.
to lose
'verlieren' and 'verteidigen' are in clear contrast, especially in sports. When a team 'verliert' (loses) a title, a place, or a lead, it no longer has it in the end. When it 'verteidigt' (defends) it, it tries to keep it and not give it up to others. So 'verlieren' describes the negative result. 'verteidigen' describes the attempt or success of protecting and keeping something.

Der Boxer verteidigt seinen Titel vor vielen Zuschauern.
The boxer defends his title in front of many spectators.
Die Mannschaft verliert in der letzten Minute noch die Führung.
The team loses the lead in the very last minute.