The violence erupted in the southern Calabrian town of Rosarno, because __

Addressing the upper house of the Italian parliament late Tuesday, Interior Minister Roberto Maroni praised the work of the security forces in the southern Calabrian town of Rosarno, where African farm workers rioted in the streets last week. [7]The two days of violence erupted after a group of white local youths allegedly shot two immigrants with a pellet gun.
    Maroni said the immediate reaction on the part of security officials from the start of the disorder ensured the violence did not degenerate into more serious incidents. [8]in all, 21 migrants were injured in the clashes, with eight still hospitalized.
    The interior minister said about 750 illegal immigrants were transferred to holding centers in the southern cities of Crotone and Bari. He added that more than 300 with regular permits left Rosarno voluntarily with their own means to other destinations. Maroni made clear the fight against illegal immigration would continue without let-up.