You will be given a definition of a task first, then an example. Follow the example to solve a new instance of the task.
In this task, you are given a question and a context passage. You have to answer the question based on the given passage.

what is the first event mentioned?, Context: The Russian Revolution is the series of revolutions in Russia in 1917, which destroyed the Tsarist autocracy and led to the creation of the Soviet Union. Following the abdication of Nicholas II of Russia, the Russian Provisional Government was established. In October 1917, a red faction revolution occurred in which the Red Guard, armed groups of workers and deserting soldiers directed by the Bolshevik Party, seized control of Saint Petersburg (then known as Petrograd) and began an immediate armed takeover of cities and villages throughout the former Russian Empire.
Solution: Russian Revolution
Why? This is a good example, and the Russian Revolution is the first event mentioned.

New input: What factor allows any player to be targeted?, Context: There are many rules to contact in this type of football. First, the only player on the field who may be legally tackled is the player currently in possession of the football (the ball carrier). Second, a receiver, that is to say, an offensive player sent down the field to receive a pass, may not be interfered with (have his motion impeded, be blocked, etc.) unless he is within one yard of the line of scrimmage (instead of 5 yards (4.6 m) in American football). Any player may block another player's passage, so long as he does not hold or trip the player he intends to block. The kicker may not be contacted after the kick but before his kicking leg returns to the ground (this rule is not enforced upon a player who has blocked a kick), and the quarterback, having already thrown the ball, may not be hit or tackled.
Solution:
possession of the football