This isn't, of course, limited to the NFL. This happens in most fields.
https://thejobsauce.com/is-landing-a-job-really-about-who-you-know/
"When you consider the hiring data available, a few statistics highlight that when it comes to landing an initial interview, it’s not what you know, it’s who you know.
Research from LinkedIn shows that in 2016, a whopping
70% of people were hired at a company where they already had a connection in place. That should be all the motivation you need to learn how to leverage your network to get referred by someone. At the most desirable companies the number is higher, with 95% landing jobs because of connections.
A study completed by Lever ATS indicated that, once interviewed,
a referred candidate has a 20x higher chance of getting hired than someone who applied online for a critical job (8.3% if referred and 0.4% if applied online). When you’re referred by a source trusted by the hiring manager, that number increases to 50x (20% of hire compared to 0.4%).
Breakdown by the numbers of who is getting hired. It all comes down to this: it’s who you know that gets you referred and interviewed as a top candidate."
It's always been more about WHO you know than WHAT you know. In almost every industry.