If the player is passing the ball ''forward'', the ball will be accelerating towards the opposition goal line for a whole series of milliseconds before the player lets it go (as it passes across and in front of his body). When he lets the ball go, it will be travelling towards the opposition goal line, faster than the player himself. If it continues to accelerate after he's let it go, that acceleration is the effect of the wind. If the air is stagnant, then the ball will begin to decelerate (towards the opposition goal line) immediately it leaves the passers hands. So you'd have to separate the motion, into before and after it parts company with the passers hands. If you want to judge a ''forward'' pass then its the acceleration (towards the opposition goal line) up until the instant the player lets it go that counts. If he's accelerating it, its a forward pass and if he's decelerating it, its a backward pass.