FOOTBALL: Referee stabs player and then gets beheaded by angry spectators

In Brazil, the country hosting the 2014 World Cup a referee was beheaded by an angry crowd after he stabbed and killed a player, who would not leave the pitch when he was given a red card. The violence erupted when ref Octavio da Silva, 20, red-carded player 30-year-old Josenir dos Santos Abreu during a game in the town of Pio XII.

The player refused to leave the pitch and an altercation broke out between the ref and Josenir dos Santos Abreu. During the tussle da Silva pulled out a knife and stabbed the unruly player. Josenir was taken to hospital however he died in the ambulance on the way there.
Spectators learned of the player’s death and charged the pitch and attacked the ref da Silva and then according to footage, they dismember his legs and cut off his head, before mounting his head on a wooden spike in the middle of the pitch.
What is your take in this shocking  evil in football? Why on earth will a referee come to the pitch with a knife?