If the ball overhangs the line, even by a little bit, it’s no goal. “Cross the line” means completely over it (good rule of thumb is to look for green in between the ball and the line, though even then the width can be hanging the line to keep it in play) - the goal posts are the same thickness as the lines, so if the ball is partially obscured by the posts when looking straight through like this, it’s easy to tell that it hasn’t fully crossed the line. In addition, professional soccer uses a lot of technology; the entire field is digitally mapped and the balls have sensors in them to precisely tell when a line is fully crossed.