How do football referees figure out where to spot the ball on an out-of-bounds punt?

I've seen the line judge walking up the sideline and someone tells him when to stop. What is he looking at and who is he working with for this play?How do football referees figure out where to spot the ball on an out-of-bounds punt?
Its basicly just guessing.How do football referees figure out where to spot the ball on an out-of-bounds punt?
They place the ball where it hit first out of bounds. They also can put headphones on and people will tell where the ball hit first.
they make a line from where the ball landed to where the ball was kicked and where it intersects the side line is the spot.
It is a guess. The ball is spotted where it crossed the out of bounds line so they look at the punter and where the ball bounced and try to draw a line. Then the put the ball where the 2 lines intersect. A great big guess.

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