Is Antioch a city or a castle in your game? It it's a city, try lowering the tax rate some. Rioting is caused by low public order. A governor with high piety and chivalry increases public order, which is probably why you get a huge drop when you move him out. Garrisons increase public order, as do certain buildings (walls, barracks, town hall line, sanitation line, inns and churches). The major causes of unrest are spies, bad traits on the governor, high taxes, and religion. Religion is likely your major cause. I expect the majority of the population is Islamic, right? Build a catholic church there and upgrade it. Build priests there and keep them in the region. Those will slowly convert the populace to catholicism. That will reduce the religious unrest.