der Schiri
referee
A colloquial short form of Schiedsrichter; a person who monitors compliance with the rules and makes decisions during a sports game.
Der Schiri hat ein klares Foul übersehen.
The ref missed a clear foul.

ref
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referee
A colloquial short form of Schiedsrichter; a person who monitors compliance with the rules and makes decisions during a sports game.
Der Schiri hat ein klares Foul übersehen.
The ref missed a clear foul.

'Schiri' is a colloquial short form of the word 'Schiedsrichter' (referee). Such shortenings are very common in spoken language.
Alle warteten auf die Entscheidung vom Schiri.
Everyone waited for the ref’s decision.
The word 'Schiri' is used almost exclusively in colloquial language and in sports reporting. In official documents or very formal contexts, you would use 'Schiedsrichter' (referee).
Der Kommentator war mit dem Schiri nicht einverstanden.
The commentator disagreed with the ref.
Common verbs used with 'Schiri' describe the referee’s actions in the game. These include 'pfeifen' (to blow the whistle), 'entscheiden' (to decide), or 'eine Karte zeigen' (to show a card).
Der Schiri pfiff das Spiel pünktlich ab.
The ref blew the final whistle right on time.
referee / arbitrator
'der Schiedsrichter' and 'der Schiri' refer to the same person in sports: someone who monitors the rules and makes decisions during the game. The difference is mainly in style. 'Schiedsrichter' is the normal, full form and also fits in reports or official situations. 'Schiri' is the short, colloquial form. It sounds especially natural in conversations about football or other games. In terms of meaning, there is no important difference here.

Der Schiri pfiff sofort, weil der Spieler im Abseits stand.
The ref blew the whistle immediately because the player was offside.
Vor dem Spiel prüft der Schiedsrichter den Ball und spricht mit den Kapitänen.
Before the game, the referee checks the ball and talks with the captains.