What does Boxing Day have to do with boxing?
The money Judas Iscariot received for betraying Jesus to the authorities. He later threw the money into the Temple of Jerusalem, and the chief priests bought the “potter's field” with it, to be used as a cemetery for foreigners.
Note: This money is referred to as “blood money” — money received for the life of another human being.
Note: “Thirty pieces of silver” is also used proverbially to refer to anything paid or given for a treacherous act.