Acceleration determines how easy you can clear off the chasing defender. Messi 79 speed and 92 acceleration fly past defenders after collecting the ball, where as Haland with 103 speed and 83 acceleration cant go past one defender
Acceleration refers to when you have the ball and speed refers to when you Chase the ball. I have kept my striker's acceleration up to 99 and speed is just 80 or below, while my defenders have speed up to 90+ and acceleration is just 65+ or below. My defenders don't have any concern with scoring goals, (i rarely score goals with them, especially in corner kicks) their job is to defend their territory only and strikers are concerned with attacks only. Thanks later 😉