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Alexander Isak was booked after taking an illegal penalty for Real Sociedad on Sunday.
La Real beat Elche 2-1 away from home, with Alexander Sorloth and Robin Le Normand completing the comeback win after Guido Carrillo put the hosts ahead.
Sweden striker Isak thought he had levelled matters in the 19th minute when he sent Edgar Badia the wrong way and put the ball in the back of the net.
It looked like a skilful spot-kick from the former Borussia Dortmund man but there were immediate appeals from the Elche players.
And then the referee promptly whistled and signalled for an Elche free-kick. He then brandished the yellow card to Isak, who looked disgusted with himself.
In real time it all happened very quickly but when slowed down, you see that Isak had used an illegal run up - completely stopping to send Baria to the floor before he stuck in his penalty.
The move was something that Mario Balotelli made famous. But because there was an absolute halt - unlike what we see from Chelsea and Italy midfielder Jorginho - Isak's effort from 12 yards breached the rules.
A section on penalty kicks on the FA website explains the situation.
It reads: "Feinting in the run-up to take a penalty kick to confuse opponents is permitted as part of football. However, feinting to kickt he ball once the oplayer has completed his run-up is considered an infringement of Law 14 and an act of unsporting behaviour to which the player must be cautioned."
The punishment for an illegal run-up has changed in relatively recent times, though. In 2011, Lionel Messi's innovative penalty against AC Milan in the Champions League was an illegal one.
Messi stopped dead during his run-up and then slotted past Christian Abbiati but the feint was not within the regulations.
Referee Wolfgang stark booked Messi but he ended up getting a retake and made no mistake on the second attempt.