Coaches spend a lot of time talking in front of their team. As such, many like to bring in outside voices whenever possible because one voice, no matter how golden-throated and full of wisdom it may be, runs the risk of turning into Charlie Brown's teacher if not peppered with some variety.
Bringing in alternate speakers is a good idea. And many of the smart coaches realize they have 85 smart, passionate and convicting voices sitting right in front of them, every single day.
Case in point, this speech from Arizona Cardinals defensive back Tyrann Mathieu, given to his fellow defensive backs and captured by the Amazon series "All or Nothing."
Do yourself a favor and watch this thing.
https://twitter.com/nfl/status/749316747275014144
"All or Nothing" is streaming for free now on Amazon.