Well, specifically what set off this specific assault were the Jews attacking Arabs who were in houses of worship during Ramadan. The Arabs weren't gonna take it lying down, so it turned into brawls, which turned into riots, which had police forces raiding and clearing houses of worship during a holy period, and Arabs getting killed.
Hamas decided it wasn't gonna stand the the infringement on their freedom of religion and attacked. Originally Posted by GastonGlock
There is no valid excuse for raining down rockets on non military targets, period.