The Jews bought the field in Judas' name, on his behalf.  It was with the money that had been given to him for his betrayal of Christ and was the same money he threw back at them.  The Jews could not use the money since it was blood money and they bought the field in his name.  This is why it says that Judas acquired the field. This idea is found in the Bible.  For example, In John 19:1 it says, "Then Pilate therefore took Jesus, and scourged Him."  But we know that it was not actually Pilate who did the scourging.  Rather it was he who handed Jesus' over to the Roman soldiers to be scourged.  They carried out his orders.