In the ensuing chaos, the Libertadores Cup last-16 second-leg tie was called off.
"We will accept the responsibility that we have but, I don't think the players are responsible," Boca president Daniel Angelici told reporters in a news conference.
The match was goalless when it was abandoned roughly an hour after the attack. River had led the two-legged tie 1-0 after last week's first match.
Players Leonardo Ponzio and Leonel Vangioni along with Matias Kranevitter and Ramires Funes Mori were the quartet of players hospitalized.