Woodbridge Vikings Head Football Coach Karibi Dede talks about the first day back at practice after the stabbing death of senior Kenneth Diaz, a member of the football team. (Brad Horn/The Washington Post)

A Woodbridge High School football player was fatally stabbed Saturday afternoon at a Prince William County park, an incident that has left his friends and teammates struggling for answers and mourning the death of the 18-year-old linebacker.

Police said Sunday that they are investigating the death of Kenny Joseph Diaz, who was found with a stab wound to the stomach in Marumsco Acre Lake Park in Woodbridge. Officers responded to a call about a stabbing victim in the park, east of Interstate 95 near the Occoquan Bay, at 3:15 p.m., police said, and Diaz was taken to a hospital, where he later died.

In a news release, police said the stabbing “does not appear to be random,” indicating that Diaz might have known his attacker or attackers. Prince William County police asked for the public’s help in providing information about the attack, the fourth homicide this year in the large suburban county.

Diaz’s death shook the Woodbridge High School community over the weekend.

“I can’t believe our school here at Woodbridge has lost a young man in such a way,” said Diaz’s football coach, Karibi Dede. He said Diaz’s family “is our family. We have to make sure we are mindful and prayerful and that we help them in any way we can.”

Just a day before the stabbing, the Woodbridge football team had basked in the glow of celebrity and victory. Scouts and media representatives attended its Friday night game against Stonewall Jackson High School, largely because Woodbridge has one of the nation’s top-ranked high school prospects, Da’Shawn Hand, who is deciding between three elite college football programs for next year. Woodbridge won, 42-34.

Then, less than 24 hours later, the unthinkable happened, Dede said.

“It was a great day, it was a very happy day, and today is a very sad day — a very contrasting mood,” Dede said of losing one of the members of the team’s 65-student varsity roster. “I think this will be very, very hard for them, I think it will be hard for our school.”

Dede said it made him think of the cautions he shares with his players. “The one thing I always tell kids is: ‘Real life is a lot tougher than football,’ ” he said.

Diaz was one of team’s reserve players. He wore the No. 43 jersey and was smaller than many of his teammates, listed at 5-8 and 191 pounds on the Woodbridge Vikings’ roster.

“He was very well-mannered, a very coachable, likable kid,” Dede said. “He was not the biggest kid, but he always gave great effort and he always supported his teammates.”

Efforts to reach Diaz’s family were unsuccessful Sunday.

Word had started to circulate among players late Saturday, and by Sunday morning, Dede said he got a call from Hand.

“Coach, is it true?” Dede recalls the top recruit asking.

Other players soon were calling and texting, and Dede said that as a group “they are pretty shaken up, pretty upset about it. Obviously, there are no easy words or answers for them at this point.”

Hand declined to comment Sunday.

“Tomorrow is going to be a tough day,” Carlos Castro, an engineering teacher at Woodbridge, said Sunday. In his seven years at the school, he recalled that one student died in a car accident and another of a medical condition. Nothing like this. “I don’t know how the school is going to react.”

Melissa Leassear, a 16-year-old junior, said Diaz was quiet, friendly and doted on his younger sister. She also said he was very religious.

“Whenever someone swore to God, he’d always say, ‘Don’t take God’s name in vain,’ ” she said.

Leassear and fellow students shared the news Sunday on Twitter, trying to make sense of it.

Leassear said she started an online movement to get students to wear red to school Monday in Diaz’s honor. It was his favorite color.

She said he talked about college on Twitter. “He once wrote, ‘You don’t have anything if you don’t have dreams,’ ” she said. “So I know he had big plans.”

Diaz’s teammates are expected to gather Monday to support one another.

“It’s going to be a tough period for everyone,” Dede said.

Dede said he knows a lot of players think two-a-day practices are hard.

But, he said, it pales in comparison to what people go through in life: “You see there are so many things harder than having to run sprints or do tackles.”

Michael Alison Chandler contributed to this report.