In this scenario, a moving soccer ball strikes a stationary soccer ball. According to the principles of conservation of momentum and Newton's laws of motion, the stationary ball will start moving in the direction of the incoming ball after the collision, and the ball that struck it will lose some of its momentum, resulting in a decrease in its speed.
Given the options, the most accurate description of the result of the collision is:
The stationary soccer ball will begin moving downfield and the ball that struck it will slow down.