Complex sentence: FIFA, the international body that oversees international association football competitions, has developed its own code of rules for indoor football (which they refer to as futsal), while indoor soccer is sanctioned by a number of national and international organizations that are unaffiliated to FIFA.
Split into simpler sentences: FIFA, the international body that oversees international association football competitions, has developed its own code of rules for indoor football (which they refer to as futsal). Indoor soccer, on the other hand, is sanctioned by a number of national and international organizations that are unaffiliated to FIFA.