After Colombia sealed a 1-0 victory in Charlotte, North Carolina, Uruguay players climbed into the stands, apparently exchanging blows with opposition fans.
Bielsa says players' family members were assaulted by Colombians in the stands. He was outraged after CONMEBOL opened an investigation into Uruguay and criticised the Copa organisers for failing to protect the families of his players.
"You know whose responsibility it is to protect the fans in the stands. You have to ask me whether the players have received an apology from those responsible for safeguarding security," the former Leeds United manager told reporters on Friday. He did not fear possible sanction, he added.
"The players reacted as any human being would have done if they saw that there was no escape or prevention and they were attacking their wife, mother, a baby," said Bielsa, who is Argentine.
"What should they do?... Nobody wants to see a violent reaction, but you have to look at what a reaction is in response to."
The South American football governing body is investigating 11 Uruguayan players, and Uruguayan sports minister Sebastian Bauza said some will miss at least the next two World Cup qualifiers in September.
"We have players who, for sure, will be suspended for the two qualifiers we have left this year (against Paraguay in Montevideo and away to Venezuela)," Bauza told Uruguay's Canal 10.
"Hopefully, it will be as few games as possible and as few players as possible."
Uruguay will play again at Charlotte's Bank of America Stadium for the Copa America third place against Canada on Saturday.