Raising and falling of share price in stock market is a question of demand and supply. To be precise, the demand and supply situation at that precise moment. If the supply is less and demand is more, share prices will rise. On the otherway round, i.e. if the supply is more and demand is less, share price will fall. Sometimes, these supplies and demands are artificially manipulated. That is what we call as price rigging. To my knowledge, there is no other explanation for it. If any one else has got better answer please post it here.