Complex sentence: Sporadic rioting occurred among the about 1000 pro-Erdoğan protesters who had come to the Turkish consulate, which was met by Dutch riot police which arrested 12 people for violent assault and not following police instructions.
Split into simpler sentences: Sporadic rioting occurred among the about 1000 pro-Erdoğan protesters who had come to the Turkish consulate. They were met by Dutch riot police, who arrested 12 people for violent assault and not following police instructions.