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Referee Massimo Busacca booking a player.
Possibly the biggest thing that went against Arsenal in the match was referee Massimo Busacca's officiating. Along with Van Persie's red card, Arsenal received an additional three yellow cards: Bacary Sagna, Jack Wilshere and Laurent Koscielny, and were called for 19 fouls compared to Barcelona's eight. Barcelona had no bookings.
According to BBC News, Van Persie and manager Arsene Wenger complained about the officiating.
"We feel betrayed a bit, when it was 1-1 it was all to play for and in my opinion this referee killed the game," Van Persie said.
"We are frustrated with his [Busacca's] decision. It is very difficult to understand his attitude," Wenger said after the match.