der Überfall
robbery / attack
A sudden, violent attack, usually with the intention of stealing.
Die Polizei untersucht den bewaffneten Überfall auf die Tankstelle.
The police are investigating the armed robbery of the gas station.

robbery / attack
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robbery / attack
A sudden, violent attack, usually with the intention of stealing.
Die Polizei untersucht den bewaffneten Überfall auf die Tankstelle.
The police are investigating the armed robbery of the gas station.

'Der Überfall' (the robbery/attack) is the noun corresponding to the separable verb 'überfallen' (to attack, to raid, to ambush). The basic idea is that someone or something suddenly 'falls over' a person or place, meaning attacks unexpectedly and often aggressively.
Die Wanderer wurden von einem Gewitter überfallen.
The hikers were caught by a thunderstorm.
The meaning is easy to recognize from context. With 'Bank' (bank), 'Geld' (money), or 'bewaffnet' (armed), it is about a robbery. With 'Armee' (army), 'Soldaten' (soldiers), or 'Land' (country), it is about war. With 'Besuch' (visit) or 'Familie' (family), it means a surprise visit.
Der Überfall auf die Schmuckhandlung dauerte nur wenige Minuten.
The robbery of the jewelry store lasted only a few minutes.
In a criminal context, 'Überfall' is often used with the preposition 'auf' + accusative. Typical verbs are 'einen Überfall verüben' (to carry out a robbery/attack) or 'einen Überfall begehen' (to commit a robbery/attack).
Die Täter haben den Überfall auf den Supermarkt monatelang geplant.
The perpetrators planned the robbery of the supermarket for months.
The use of 'Überfall' for an unannounced visit is colloquial and usually meant ironically or as a slight exaggeration. It expresses that one feels overwhelmed by the spontaneity.
Sorry für den Überfall, aber ich war gerade in der Nähe.
Sorry for dropping in on you like this, but I was just nearby.
visit / visitor
'der Besuch' and 'der Überfall' can both have to do with people coming somewhere, but their normal meanings are very different. 'der Besuch' is neutral or positive: someone comes to see a person or goes to a place and stays for a while. 'der Überfall' usually means a sudden, violent attack, often during a robbery. Colloquially, 'Überfall' can also be used jokingly or critically for an unannounced visit. Then it sounds as if the visit was surprising and perhaps disruptive. For that reason, the words can only be confused in this colloquial meaning.

Der spontane Überfall meiner Freunde hat mich zuerst erschreckt, aber dann haben wir zusammen gekocht.
The spontaneous surprise visit from my friends scared me at first, but then we cooked together.
Heute Abend bekommen wir Besuch von unseren Nachbarn.
We're having a visit from our neighbors this evening.