In a crucial relegation encounter in the Bundesliga, Winkmann blew the half-time whistle with the game goalless.
However, as the players headed off, the official consulted VAR after a late incident inside the penalty box.
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After VAR noticed Freiburg defender Marc-Oliver Kempf had blocked a shot with his arm, the referee duly awarded Mainz a penalty – though they could not take it until the Freiburg goalkeeper had come back from the dressing room.
Eventually, Alexander Schwolow made his way back onto the pitch, but conceded the spot-kick to Pablo de Blasis in what turned out to be the 52nd minute of the first half.
Cue the toilet roll protests at half-time.
Mainz v Freiburg
Image credit: Eurosport
VAR is set to be used at the World Cup, though Premier League clubs decided against using it in the 2018-19 season after deeming that more testing was required.
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European round-up: Athletic Club suffer home defeat to Cadiz; Gladbach draw at Mainz
1. FSV Mainz 05