der Kapitän
captain
The person who has command of a ship or airplane and bears responsibility for it.
Der Kapitän steuerte das Schiff sicher durch den Sturm.
The captain steered the ship safely through the storm.

captain
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captain
The person who has command of a ship or airplane and bears responsibility for it.
Der Kapitän steuerte das Schiff sicher durch den Sturm.
The captain steered the ship safely through the storm.

'Der Kapitän' (captain) is a weak noun (N-declension). This means it takes the ending '-en' in all cases except the nominative singular.
Die Mannschaft vertraut dem Kapitän_en_.
The team trusts the captain.
You can tell from context whether a ship/airplane captain or a sports captain is meant. Words like 'Schiff' (ship), 'Flugzeug' (airplane), or 'Crew' (crew) point to the commander, while 'Mannschaft' (team), 'Team' (team), or 'Spiel' (game) point to the athlete.
Der Kapitän der Nationalmannschaft gab nach dem Spiel ein Interview.
The captain of the national team gave an interview after the game.
In a maritime or aviation context, 'Kapitän' (captain) is often connected with verbs like 'steuern' (to steer), 'navigieren' (to navigate), or 'das Kommando haben' (to have command). A typical location phrase is 'auf der Brücke' (on the bridge).
Der Kapitän hat das alleinige Kommando auf der Brücke.
The captain has sole command on the bridge.
In a sports context, the most common combination is 'Kapitän der Mannschaft' (captain of the team). An important symbol is the 'Kapitänsbinde' (captain's armband), which the captain wears on the arm.
Er wurde zum neuen Kapitän der Mannschaft ernannt und trug stolz die Kapitänsbinde.
He was appointed the new captain of the team and proudly wore the captain's armband.
trainer / coach
'der Trainer' and 'der Kapitän' can both be important people on a sports team. The coach leads training, plans tactics, and looks after the players. He does not have to play himself. The captain, on the other hand, is a player on the team and leads the team during the game, often with an armband. The words can be confused because both have responsibility and can give instructions. In sports, the rule is: the coach usually stands on the sidelines, while the captain plays on the field.

Der Kapitän spricht kurz mit dem Schiedsrichter und führt dann sein Team aufs Feld.
The captain speaks briefly with the referee and then leads his team onto the field.
Der Trainer erklärt der Mannschaft vor dem Spiel die neue Taktik.
The coach explains the new tactics to the team before the game.