Try to follow this train of thought....

A pro is someone who gets paid to do a job as earlier explained.

I am in the military thus I am a professional airman.

All military personnel are paid 24/7/365 because defending this great nation is not a 9 - 5 job.

Since I am paid 24/7/365, when I take leave (vacation) I am still getting paid.

Since I hunt while on leave, I am being paid to hunt.

Therefore, I am a professional hunter.

Now for endorsers, which is quite a bit easier to explain...

All military personnel are paid by the federal government.

All federal money comes from taxes.

Taxes are paid by all people earning income.

Therefore, every tax payer (which includes the majority here) is my sponsor.

Thanks guys.