Why was a World Cup referee drinking pickle juice?
Referee Felix Zwayer used pickle juice to treat a cramp during the USA-Australia match, a common remedy in professional sports.

BBC Sport
The USA's 2-0 victory over Australia at the World Cup featured an unusual incident in stoppage time when referee Felix Zwayer collapsed to the ground with a cramp. As the match was halted, the official required assistance from players and his colleagues to stretch his leg.
In a moment that caught the attention of fans, the fourth official, Katie Garcia, ran onto the pitch to provide Zwayer with a carton of pickle juice. After consuming the brine, the German official was quickly able to get back to his feet and complete the match.
Pickle juice is a common recovery tool in professional athletics. It contains high levels of sodium and potassium, which are believed to disrupt the neural signals that cause muscles to cramp. Studies suggest this brine can stop cramping up to 40 per cent faster than water by triggering a reflex that signals muscles to relax.
While the drink is known for its strong, tangy taste due to vinegar and herbs, its effectiveness during intense heat or exhaustion has made it a staple in sports ranging from the NFL to elite tennis. It is designed to be taken after the onset of pain, providing a rapid boost to help athletes manage fatigue and circulation during demanding matches.