Learn German: Er wehrt sich gegen jede Kritik. - He defends himself against every criticism.

The reflexive verb sich wehren (to fight back / to defend oneself) is a fixed phrase that always takes the preposition gegen (against), which in turn always requires the accusative case. It implies actively resisting something.

Is there a difference between sich wehren and sich verteidigen?

Yes. While both can be translated as 'to defend oneself', sich verteidigen is often about arguing your case or justifying yourself. sich wehren has a more defiant, resistant feeling, like pushing back or refusing to accept the criticism.

Why does the sentence use jede Kritik instead of alle Kritik?

While English often says 'all criticism', German prefers jede (every) for singular, abstract nouns to mean 'any and all' of it. Saying alle Kritik isn't strictly wrong, but jede Kritik sounds much more natural and emphatic here.

Why does jede have an '-e' at the end?

The preposition gegen always forces the following noun phrase into the accusative case. Because Kritik is a feminine noun, the determiner takes the feminine accusative ending, giving us jede.