What made chariot racing dangerous?

Chariot racing was an extremely dangerous sport, and the driver always had a high risk of getting thrown from the open chariot or trampled or dragged to his death. It was quite common as a large number of riders got caught in the reins.
Also, the chariots were quite heavy and hence needed a great degree of skill to avoid toppling over or handling difficult terrain. Even though the same was considered an adventure sport yet the same was not entirely easy to use daily.