In the discussion about impulse and force in a pitcher-catcher fastball, the focus is on understanding which player exerts a larger impulse and force on the ball. It is established that the pitcher exerts a larger impulse on the ball due to the acceleration provided during the pitch. Conversely, the catcher exerts a larger force when catching the ball, as he must apply a force to stop its motion. The conversation emphasizes the importance of analyzing the three phases: start, in-flight, and end, to clarify the concepts. Overall, the discussion highlights the relationship between impulse, force, and the roles of the pitcher and catcher in the fastball scenario.