Answer:
Newton's Third Law
Step-by-step explanation:
Newton's Third Law stipulates that for every action there is an equal and opposite reaction.
So when the two players are tackling they exert a force on each other.
If player 1 tackles (exerts a force) player 2, player 2 will exert an equal and opposite reaction on player 1 as stated in Newton's Third Law.
Therefore when they tackle each other so hard they both experience reaction forces so powerful that they fly in opposite directions.
Thus this is an example of the Newton's Third Law.