How do you tell how fast a player's character is moving at one specific point in time (Not walkspeed as that only states a players maximum speed, and is fixed)
Check the velocity of any part in the character. Velocity is how far something moves in one second, and speed is Velocity.magnitude.
Try player.Character.PrimaryPart.Velocity or player.Character:FindFirstChildOfClass('BasePart').Velocity
Take the position of a player, wait 3 seconds, take the position again, use the difference equation. That is their distance traveled per 3 seconds.