The incident unfolded during a Japanese attack. With the referee's back turned, the Brazilian pushed him and then struck him on the back, before carrying on his run towards the loose ball in what looked like an attempt to clear the official out of his path.
Jinson Fu turned and looked at Endrick, yet did nothing. No yellow, no red. That opened the door to questions over how the act went unpunished, particularly as it involved the referee himself.
Attention swung back to the striker's situation at Real Madrid, where he rarely starts and often comes off the bench, despite coach Jose Mourinho's insistence on keeping him and his refusal to sanction a departure in the face of the offers the player has received.
Endrick's moment wasn't the only flashpoint. Raphinha was sent off after protesting the referee's decisions following his substitution in the 71st minute, and Ancelotti followed him down the tunnel for his own objection, adding to a string of incidents on a night that ended in yet another defeat for the Brazilian national team.
From the substitutes' bench, Raphinha watched a late Japanese goal settle the result before venting his fury at the refereeing and branding the decision "unacceptable". The suspension rules him out of Brazil's upcoming match against Singapore.
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The winger decided to stay with the national team's delegation regardless, as confirmed by Rodrigo Caetano, chief executive of the Brazilian Football Confederation. It comes at a difficult time for the Barcelona player, who had been forced before the match to defend his commitment to club and country amid criticism of the injuries he suffers during international breaks.
Ancelotti's sending off increases the pressure on Brazil
All of this lands in a tense atmosphere around the Brazilian national team, with results tailing off under Ancelotti and the criticism aimed at him growing louder, despite his glittering coaching record.
The Italian has 12 wins, five defeats and four draws from 21 matches, a win rate of 62%. Tite managed 86% and Carlos Dunga 81%.
Vinicius Junior, by contrast, drew praise after scoring both Brazil goals against Japan, with the comparisons underlining how his situation differs from that of Raphinha, who is producing notable numbers for Barcelona. Raphinha has 12 goals in 44 internationals, against 16 for Vinicius in 58.
The criticism spilled off the pitch too. Former Brazilian star Romario called for Ancelotti's departure, arguing that for all his club successes the coach has yet to prove he can lead the national team, and warning against another World Cup failure.
So the defeat to Japan was no ordinary negative result. It left behind more than one thorny issue, topped by Endrick's clash with the referee, an incident that spilled well beyond the pitch and became the focus of controversy long after the final whistle.
