What is a skewed start line?
So in this illustration we start our sailboat race with a Square Line, then you will see that if the pin end is moved closer to the Windward Mark, the line is no longer at a 90 degree angle with the wind or the mark (in this case the two are the same). That gives the advantage to the boat starting at the Pin End of the line, at least geometrically. In theory, all things being equal, the red boat will cross ahead of the black boat because they started further up the course.
As represented here, this puts the red boat at a rules disadvantage because they will be crossing the black boat on port while the black boat is on starboard. Although if the advantage is enough and the red boat has enough speed, they could get by the black boat. This is known as “port tacking the fleet” – one of the riskiest and most rewarding moves in sailboat racing.