ATLANTA — Before he was the best football coach of this generation, before he led the New England Patriots to eight Super Bowls in 19 seasons — with a ninth appearance on tap Sunday against the Los Angeles Rams — Bill Belichick was part of the grassroots movement that brought lacrosse to Michigan.

Belichick spent two seasons as an assistant with the Detroit Lions in his second job out of college. He was assistant special teams coach on Rick Forzano’s staff in 1976, the team’s tight ends coach a year later, and during his downtime in the spring, Belichick coached lacrosse as a volunteer assistant at Birmingham Detroit Country Day.

“That was a great experience for me,” Belichick said at Super Bowl LIII this week. “It was fun to continue to be involved in the sport of lacrosse, in a different community, outside of Maryland or Connecticut where I played. … At that time the sport was — it’s obviously grown a lot since then, but it was growing into those areas and was fun to be part of the areas outside of kind of the traditional ones, developing it as a sport.”

Belichick’s time at Country Day is neither well chronicled nor well remembered by those in the program, though more than 40 years later some vivid memories remain.

Belichick grew up in the lacrosse hotbed of Annapolis, Md., and played both lacrosse and football in college at Wesleyan.

He was a team captain in lacrosse. He played defenseman, attack and as a backup goalie. And to no one’s surprise, one of his former rivals and current friends said he was very much a coach on the field.

“He was an excellent player,” said Kevin Spencer, who played both football and lacrosse at Springfield (Mass.) College and now works as a football analyst on the coaching staff at Iowa. “It’s funny, I tell people that we used to get scouting reports and they’d say Belichick could go right, left, blah, blah, blah. And then they’d say, ‘Coach on the field.’ Didn’t have great speed, but he was — the guy that ran the team was a soccer coach, and he really probably did it just so they would have a team. So Bill had himself and there was a contingent of guys from Annapolis that went to school there and they kind of, respectfully, ran the team.”

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Belichick, whose father Steve played briefly with the Lions and was a longtime assistant at Navy, spent one season as a low-level assistant with the Baltimore Colts before Forzano brought him to Detroit.

Spencer happened to be in Michigan at the time, as a coach (of just about every sport) and middle school athletic director at Country Day.

“We were practicing one day and this guy comes walking down to the practice field and I looked at him and I go, ‘That’s Bill Belichick,’ ” Spencer recalled. “And he looks at me and he says, ‘You’re Spencer from Springfield, right?’ So you kind of remember competing against the guy, but it wasn’t like you were bosom buddies and went and had a beer with him.”

To this day, no one remembers exactly how, when or why Belichick showed up.

Country Day’s head lacrosse coach at the time was Gene Reilly, who coached lacrosse and football at Wesleyan before Belichick arrived on campus. Spencer said perhaps the Wesleyan connection led Belichick to Country Day in what he remembers as a spring day in 1976.

Reilly, who’s now retired and lives in Florida, said he didn’t know Belichick until that first practice, though their Wesleyan connection did lead to an instant bond.

“I think he just showed up with a lacrosse stick and introduced himself,” Reilly said. “I knew of his dad, I didn’t know him. But he was great. He read in the paper or something that we had lacrosse going on. He said, 'I was shocked and I just took it upon myself to come out.' I said, ‘Oh, great.’ He said, ‘Do you mind if I come out a few days a week?’ I said, ‘No.’ I said I need another good assistant coach.”

Dave Phillips, a former Country Day lacrosse player who went on to start the lacrosse program at Novi Detroit Catholic Central, said he remembers Belichick being a part of the program only in the 1977 season, and that Belichick picked Country Day because a Lions coach had children who attended the school and played lacrosse at a younger age.

Whatever the specifics, Belichick was around the team in a regular but unofficial capacity.

He often attended practices but didn’t always make games because of his coaching duties with the Lions, and he doesn’t appear in a photo of the 1977 team that exists in Country Day’s archives.

“I know he did come and watch games,” Spencer said. “We provided him with a schedule and I’m sure he, as only Bill would do, he sneaks in the back door and goes out the back door. It’s not like today where he can’t go anywhere, ‘There’s Bill Belichick.’ ”

Because he was just Bill Belichick then, and not Bill Belchick The Best Coach In The NFL, Phillips was the only one of a handful of players contacted from the 1977 team who recalled Belichick coaching at Country Day.

“Belichick coached the attackmen and I was an attackman,” Phillips said. “And it’s funny, I’ve been coaching since I got out of school and when a big game, like tournament final games, or if I have a new team, I’ll always pull out the Belichick card, he was my lacrosse coach. And the expressions on these kids’ faces, it’s great. Like, ‘You’re lying.’ "

Phillips said he saw glimpses back in his high school days of the great coach the NFL world has come to know — a surefire Hall of Famer who has led the Patriots to 16 consecutive seasons with double-digit wins.

Belichick stressed playing with the proper technique, helped his players outsmart the other team — Phillips said Belichick encouraged him not to wear arm pads in order to bait defenders into trying to chop his arms, so he could beat them when their focus was elsewhere — and shared a coaching philosophy that Phillips has since heard associated with Belichick: to play mad, as in make a difference, not be angry.

“The little mind games that you hear about now, I kind of reflected upon some of the stuff he said back then,” Phillips said. “And again, he was just a kid so he wasn’t Bill Belichick yet. And that’s, I don’t know, as I look back now I’m like, ‘OK, now it’s Bill Belichick.’ ”

Belichick the lacrosse coach had a significant impact on the lives of both Reilly and Spencer, too.

Reilly launched the Country Day lacrosse program a few years before Belichick’s arrival, but with just a handful of lacrosse programs in the state at the time, it was in those early years that the seeds were planted for the booming sport of today.

And Spencer called his chance encounter with Belichick “the great hookup of my entire life.” Belichick helped Spencer land the head coaching job at Wesleyan, which he held for five years, and brought Spencer with him to the Cleveland Browns when he took over as head coach in 1991.

“I would not have had this kind of career had it not been for Bill Belichick, without a doubt,” Spencer said. “He’s tough, he’s a stern taskmaster to say the least, but if you want to learn the game of football, that’s not a bad guy to learn it from. Lacrosse, too. What’s the old expression, he’ll take his and beat yours and he’ll take yours and beat his? That’s the kind of coach he is.”

Belichick this week said his experience at Country Day was “fun” and that “I enjoyed my relationship with the kids.”

Coaching lacrosse at Country Day, in fact, meant enough to him that when the Patriots came to town for a 2017 preseason game, Lions general manager Bob Quinn and his then chief of staff, Kevin Anderson, reached out to the school to get a sweatshirt to present to Belichick, their old boss.

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Phillips said he marvels sometimes that one of the greatest coaches in NFL history was fleetingly a part of his life and played a small role in popularizing the sport in Michigan.

“Pretty much every time he’s on and he opens his mouth I think about it, there’s no doubt about it,” Phillips said. “Why didn’t I realize this guy was this guy 40 years ago?”

Contact Dave Birkett at dbirkett@freepress.com. Follow him on Twitter @davebirkett. Read more on the Detroit Lions and sign up for our Lions newsletter.