We sat down with Seth Greenwald -- who happens to be a coach himself at Hamline University now -- a few days after Walz was announced as Harris' running mate ... and he described the ex-Mankato West High School (MN) football team's leader as a "guy's guy."

"He was energic, super knowledgeable," Greenwald said. "He wants to be hands-on, whatever he's doing he's got 10 toes down. That's the thing that stands out for him. He's the same guy then as he is now for the most part, obviously he has evolved and he's taken on different roles."

Walz walked the sidelines at Mankato West for several seasons in the '90s before shifting gears ... and now with his opportunity to help steer the entire country, Greenwald spoke highly of his leadership.

"The thing that stands out is just trying to get the most out of you, trying to realize that there's a bigger picture out there and a higher goal, and pushing you to achieve your full capacity. That's really what stands out."

You can argue the biggest question people have doesn't involve the political stance of Walz -- which of course is important -- but what type of scheme did he run?

Greenwald described it as classic downhill football!!!

"It was a 4-4 cover three, it's like day one, put it on the whiteboard," he said. "We had a lot of talent. We didn't see a lot of variation of the scheme. You saw a lot of people leaning into each other. A lot of people coming downhill. So you had to be ready for the physicality, and that's kind of where the mentality comes in."