Francesco Acerbi was enraged with Barcelona defender Inigo Martinez after the Hakan Calhanoglu penalty, because video shows he spat at the Inter defender.
It was clear that Acerbi was furious with Inigo Martinez straight after the conversion of the spot-kick, which gave Inter a 2-0 lead on the night in their Champions League semi-final, 5-3 on aggregate.

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Only later did it become apparent what had sparked his anger, as the Barcelona player was caught on camera seeming to spit at Acerbi as he ran past to celebrate the goal.
Inigo Martinez seemed to spit at Acerbi
Referee Szymon Marciniak spoke to the VAR officials, but they were unable to definitively identify the incident in time to take action, which would’ve seen Inigo Martinez sent off.
It is possible UEFA can retroactively take disciplinary steps to ban Inigo Martinez for his unsporting behaviour.

Nonetheless, if the moment had been missed and Inter had gone out of the Champions League, it would’ve been seen as a failure of VAR not to send the player off.
Inter eventually won the tie 7-6 on aggregate, with a 5-4 victory in extra time on the night.