The head of the Brooklyn Young Men’s Hebrew Association was viciously attacked by hate-mongers outside the Barclay’s Center after a game and celebration honoring the Israel Defense Forces, the Post has learned. Leonard Petlakh, 42, was inside the arena with his children and friends for the Nets-Maccabi Tel Aviv basketball game on Tuesday night, when a group tried to disrupt the event by unfurling the Palestinian flag, according to a statement released by the Kings Bay YMHA. An argument broke out between several groups and people were asked to leave. As Petlakh was walking out with his children, video captured...