Junior defenseman Chris Fennell and Navy boast the No. 2 scoring defense in the country (7.13 goals per game). (Phil Hoffmann /Courtesy of U.S. Naval Academy)

The debate in the Fennell household in Millford, N.J., rages on: From where did middle child Chris get his athletic genes? His father did not play organized sports beyond eighth grade. His mother did not play sports after high school.

Of his two siblings, his older sister was in a singing group in college and recently was accepted to medical school. His younger sister was a high school cheerleader and is the artist of the family.

And then there is Chris Fennell, a junior and the top defenseman on the Navy lacrosse team. He will be in the spotlight when the unseeded Midshipmen (11-4), in the NCAA quarterfinals for the first time since 2008, face No. 5 Brown (15-2) on Saturday in Providence, R.I.

Navy enters with the No. 2 scoring defense in the country (7.13 goals per game). The Bears have the No. 1 scoring offense, at 16.7 goals per game.

Irene Fennell said her son was walking by the time he was nine months old. But explaining how he became one of the top defensemen in the nation is a little tricky.

“It’s exciting for us,” she said. “We knew nothing about lacrosse and not much about college sports in general. We always joke about his athleticism. . . . We’re just proud and happy he got whatever athletic genes he did.”

Fennell’s athleticism will come in handy on Saturday: He will be matched against junior Dylan Molloy, the nation’s leading scorer (60 goals, 54 assists). Molloy is uncommonly big for an attackman – 6 feet, 220 pounds. Navy will counter with Fennell; he is 6-2, 211 pounds and is the two-time Patriot League defensive player of the year.

“They’re an unbelievable team,” Fennell said of Brown. “They’ve had a lot of success this year. They’re a pretty tough and hungry team that’s definitely looking to prove something. But I mean, so are we. We aren’t afraid to go play anybody. It’s a great opportunity to match ourselves against a top five team and see what we’re made of.”

Fennell excels using the athleticism that manifested itself when he was a standout quarterback in a single-wing offense at Delaware Valley High in Frenchtown, N.J.

He was recruited for football primarily by Ivy League and Patriot League schools but also drew attention from nearby Temple and Rutgers.

“It was a very unique offense,” Fennell said. “I couldn’t throw the ball that well but we ran a lot, so it fit my skill set.”

Lacrosse has fit his skill set as well.

Fennell started on defense as a freshman in 2014. Against No. 1 Loyola that year, Fennell drew the assignment of guarding senior Justin Ward, the Greyhounds’ quarterback. On the opening possession, Fennell forced a turnover by checking the stick out cleanly out of Ward’s hands.

But in the third quarter, Fennell tried to make a quick cut and his ankle was caught in the artificial turf. He fell to the ground with an injury so gruesome that one teammate became sick to his stomach. However, Loyola players said later that they had never seen an injured player remain so calm.

Fennell jokes that he heard his ankle snap “like a supple tree branch” and then moved his leg and his ankle followed “about three minutes later.”

“It was pretty disgusting,” said Navy junior Matt Rees, a starting longstick midfielder. “Guys didn’t really want to go over and look at it. But Chris was lying on the field and all he was saying was, ‘Guys, I think I broke my leg.’ He was so calm and collected about it.”

Fennell’s season was over. But his surgery, initially scheduled for the following Friday, was postponed at Fennell’s request: He wanted to travel with the team to West Point, N.Y., for his first look at the Army-Navy game.

His demeanor had an added benefit for his parents, who missed the game to attend the final concert of his older sister’s a-cappella group at Colgate.

“We got a call from Chris saying, ‘I broke my leg,’ ” Irene Fennell said. “He was so calm. . . . We were sick but talking to Chris made us feel better. Susie Rees [Matt’s mother] sent me a picture at the end of the game, he had some sort of cast on and he was smiling so we felt he was okay. Later we saw the video. Everyone said it was a good thing I wasn’t there.”

Fennell is fully healed thanks to a six-inch plate and 13 screws in his ankle. He remains a tough customer. In a scrimmage against Syracuse last October, on a clear Sunday morning in a practically empty Navy-Marine Corps Memorial Stadium, the only sound was Fennell correcting a teammate who had cleared the ball too close to the Syracuse sideline.

“He definitely isn’t afraid to tell you when you’ve made a mistake,” Matt Rees said.

Said Irene Fennell: “He doesn’t baby people. . . . I’m a mom, I tell him people have feelings and people have bad days. He can be pretty tough, but he’s a good kid and he’s really funny. He definitely gets that from his father. I’m more of a laugher. He and his father are the funny ones.”