In section B of the course regulations I'm a little confused about rule #7. What is the need for a golf sized umbrella? How would a shooter hold the umbrella while shooting? Am I missing something?

It could be to keep the glare off of someone's sight. Usually another person in the group would hold the umbrella (not the shooter) as that would be a little hard (ha).

You use it to block the wind. Your buddy holds it for you.