niederschlagen
to knock down
To violently hit someone or something to the ground, often until they lose consciousness.
Der Boxer schlug seinen Gegner in der dritten Runde nieder.
The boxer knocked down his opponent in the third round.

to knock down / suppress / be reflected
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to knock down
To violently hit someone or something to the ground, often until they lose consciousness.
Der Boxer schlug seinen Gegner in der dritten Runde nieder.
The boxer knocked down his opponent in the third round.

'Niederschlagen' is a separable verb. The prefix 'nieder-' comes at the end in a main clause. In subordinate clauses and in the infinitive with 'zu', the verb stays together.
Die Regierung schlug den Aufstand nieder.
The government suppressed the uprising.
The verb consists of 'nieder' (down) and 'schlagen' (to hit/strike). The literal meaning 'to knock to the ground' is often used metaphorically to mean ending or suppressing something by force.
Die vernichtende Kritik schlug ihn emotional völlig nieder.
The devastating criticism completely knocked him down emotionally.
In the meaning 'sich auswirken' (to have an effect), the verb is always reflexive and is used with the preposition 'in' and the dative. The structure is: something (nominative) 'schlägt sich in' something (dative) 'nieder'.
Die positive Stimmung schlägt sich in den Verkaufszahlen nieder.
The positive mood is reflected in the sales figures.
In political or social contexts, 'niederschlagen' (to suppress) is often combined with abstract nouns such as 'Aufstand' (uprising), 'Protest' (protest), 'Rebellion' (rebellion), or 'Demonstration' (demonstration).
Die Armee hatte den Befehl, die Rebellion niederzuschlagen.
The army had orders to suppress the rebellion.
In legal usage, 'niederschlagen' means to discontinue proceedings. Typical objects are 'das Verfahren' (the proceedings/case), 'die Anklage' (the charge/indictment), or 'die Ermittlungen' (the investigations).
Die Staatsanwaltschaft schlug das Verfahren gegen ihn nieder.
The public prosecutor's office dropped the case against him.
The meaning 'sich absetzen' (to settle/precipitate) is a technical term from chemistry. Here the verb is often used reflexively when a solid substance separates out of a liquid.
Beim Abkühlen der Flüssigkeit schlug sich ein weißer Feststoff nieder.
As the liquid cooled, a white solid precipitated.
to hire / adjust / stop
'einstellen' and 'niederschlagen' can both express that something is officially ended. Here, 'einstellen' is more general and fits an activity, a service, or also a proceeding that is not continued. 'niederschlagen' is more specific in this meaning and sounds legal: a proceeding or investigation is ended without a judgment or result. The words can be confused because in both cases, people do not continue. 'einstellen' is more natural for many general situations, while 'niederschlagen' is more common in legal or official texts.

Das Gericht schlägt das Verfahren nieder, weil die Beweise nicht ausreichen.
The court drops the case because the evidence is not sufficient.
Die Behörde stellt die Untersuchung ein, weil es keine neuen Hinweise gibt.
The authority is discontinuing the investigation because there are no new leads.