Complex sentence: They filed a lawsuit challenging FIFA's decision to play on artificial turf, claiming FIFA would never allow the men's World Cup to be played on "unsafe" artificial turf and thus the organizers had violated the Canadian Human Rights Act.
Split into simpler sentences: They filed a lawsuit challenging FIFA's decision to play on artificial turf. The lawsuit said FIFA would never have the Men's World Cup held on "unsafe" artificial turf and thus violates the Canadian Human Rights Act.