The Democrats will be hoping that Walz, 60, can do the same part-way through their own election season as they call him off the subs’ bench and on to the field as their new vice-presidential candidate.

Now the governor of Minnesota, Walz spent more than a decade of his career as a geography, history and government teacher, mostly in Mankato, then a town of about 40,000 people with a big farming community. Former students remember a man with bouncing enthusiasm who couldn’t stop socialising, who acted as a fatherly figure and set high standards for others.

While Republicans are saying that his Midwestern niceties and charm are an act that disguises dangerous left-wing policies, his own team is pushing the football persona hard, with his running mate Kamala Harris calling him loudly, proudly and often: “Coach Walz”.

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The Scarlets’ former head coach Rick Sutton, 62, met Walz when the future politician first moved to the town with his wife, Gwen, from Nebraska, helping them unpack the removal van.

“Very early on in that conversation I knew I wanted him on my staff [on the football team],” he said. “He is obviously very genuine in what he does and you could tell immediately he cared.” Where Sutton was the “disciplinarian”, Walz brought “energy and enthusiasm’ as the team’s defensive co-ordinator.

The football team, at that point, was a little ropey. They lost 27 games straight when the two coaches started their first season together in 1996. “What was so frustrating for us was that expectations were so low — from players, parents, student body, faculty, community,” Sutton said. “We had to fight through that. Then we had to convince our players to be more dedicated, to take weight training more seriously, to work out in the off season.”

The team trained every night after school for two hours until about 6pm. They piled into an old yellow school bus to go to their Friday night game, then Sutton, Walz and their wives would often have dinner at one of their homes. There would then be a debrief on Saturday morning, back at school. “It is two full-time jobs,” said Sutton, who also taught English.

It wasn’t until the 1999-2000 season that things started going right for the team. One of the players, Considine, remembers the motivational pre-game speeches from Walz: “He had high standards for us and did a great job motivating young men to do their absolute best.”

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Excerpts from a school yearbook. Students recall his boundless enthusiasm

Walz spent most of his teaching career in Mankato, Minnesota

Their state victory was “pure jubilation”, Considine said. “It was unheard of. We were absolutely beside ourselves, nursing our turf burns from playing on the Metrodome [stadium, Minneapolis] AstroTurf.” The team had a police escort when it arrived back in Mankato. “I don’t think we would have won that state championship if we hadn’t lost at the beginning of the season,” Walz said in his 2021 State of the State address.

Bryce Tillman, 40, then offensive guard, now an engineer, remembers Walz’s “integrity”. “There are two rival high schools in the town, East and West,” he said. “The West was the team that played with heart, not taking cheap shots, not trying to get away with stuff the refs wouldn’t see. East had a tendency to get away with that stuff but Walz was always very adamant about not stooping to that level. [He’d say:] ‘Keep your integrity.’ ”

At school, Walz was relentlessly sociable, standing in the middle of the corridor outside his classroom to chat to students between lessons. Some would cut their lunch break short to go to his room. When he taught government, he created a class project in which students had to pitch a new bill — and took his class to rallies supporting John Kerry and George W Bush during the 2004 presidential election.

Nate Hood, 40, a city planner in St Paul, Minnesota, played defensive tackle and was also in “Mr Walz’s” geography class. “He was known for being a joker,” Hood said. One time, when he was teaching Hood basketball in seventh grade, they all watched him dunk the ball (slamming it in from above the basket). “We couldn’t believe he just did that, we were so impressed,” he said. “Until we realised he had lowered the hoop.”

Walz was born in West Point, Nebraska, a town of about 4,000 people, where he played football through high school. After joining the Army National Guard, though Republicans point out that he never served in a combat zone, he went to Chadron State College and then became a high school teacher, where he met his wife and began his football coaching career. They have two children, Hope, 23, and Gus, 17. In 2006 he was elected to the House of Representatives for Minnesota and re-elected five times, before becoming governor in 2018.

With Kamala Harris on stage at a rally in Philadelphia last week

ALEX WONG/GETTY IMAGES

Dan Clement, 43, a linebacker with the Scarlets, said that Walz was the first father figure he ever had. “Other folks had written me off because I’d been skipping school, getting suspended, getting detentions, drinking and drugging,” he said. “Until I met Mr Walz at football training and he was a big fan of mine for whatever reason. I was a decent player but I wasn’t the greatest guy on the field. But I just gravitated to him and I wanted to do whatever he needed.”

In his final year, Clement dropped out of the football team, “distracted” by substances and drinking. “He came to find me every day in the hallway saying, ‘Dan, we need ya, Dan we need ya, come back.’ And because of that, part-way through the senior year, I went back to the team. I was so happy he talked me into it because things were going off the rails otherwise for me. He wouldn’t let me walk away.”

Clement continued: “I responded really well to structure, working out in the weight room. and I only did them because I wanted to do well for Coach Walz.”

He believes the politician was “critical” to his eventual graduation. Clement now owns his own logistics business. “Mankato was stoic, keep it to yourself, don’t get out of line,” he said. “So Walz was kind of a fish out of water: big personality, outgoing, interested. He just pulls you in whether you like it or not.”