WATERVILLE — Jack Sandler, the head men’s lacrosse coach at Colby College since 2013, died unexpectedly Thursday. He was 35.

Sandler collapsed while on a treadmill in a hotel, according to information released Friday by Colby. In a letter to the Colby community, President David A. Greene said Sandler was on a recruiting trip out of state when he died.

Sandler came to Colby following eight seasons as the head coach at Skidmore College. He coached three United States Intercollegiate Lacrosse Association Honorable Mention All-Americans and the New England Small College Athletic Conference (NESCAC) Rookie of the Year in 2014. In 2014, Sandler’s first season at Colby, the Mules won the CBB (Colby-Bates-Bowdoin) title.

“Jack was incredibly energetic and warm,” Colby director of athletics Tim Wheaton said. “He was a classic NESCAC Renaissance man, where he cared a great deal about a sport and loved it, but also loved everything surrounding the sport at his school.”

Colby held an informal remembrance for Sandler on campus Friday afternoon, Wheaton said. Current and former players joined members of the college community to console one another and share their memories of the coach.

Wheaton said the players were hit hard by the news.

“We have young people experiencing the loss of someone who was relatively young himself. It’s a shock,” he said.

A 2002 graduate of Bates College in Lewiston, Sandler started his coaching career at his alma mater. A Long Island native, Sandler was a three-sports athlete in lacrosse, football and wrestling at Friends Academy.

“Jack was a truly great, trusted friend. More like a son in many respects,” said Bates head coach Peter Lasagna, who coached Sandler and then hired him as an assistant coach. “I am deeply saddened by the loss of this great young man and dear friend.”

Sandler was a four-year starter for the Bates Bobcats, and finished as the program’s second all-time leading scorer with 199 points. Sandler was the 1999 NESCAC Rookie of the Year and earned All-NESCAC honors during his career.

“It was clear he loved the game of lacrosse and coaching, but his real passion was teaching and helping students develop their full potential physically, intellectually, and personally,” Greene wrote in the letter to the Colby community. “We have been incredibly fortunate that Jack has been such an integral part of our community. I join others who will miss him greatly, and our thoughts are with his players, colleagues, and family.”

In his relatively short time at Colby, Sandler molded his players into well-rounded students and athletes and the lacrosse program into a vehicle for young men to strive to become not only the best lacrosse players they could be but the best people they could be.

“He really affected the culture of the lacrosse team,” Wheaton said. “They are the embodiment of what he believed in.”

Funeral services are scheduled for Monday in Glen Cove, New York. Wheaton said Colby plans to hold another memorial for Sandler some time between Thanksgiving and Christmas, on a date to be announced.

Wheaton said there are no immediate plans to name a new men’s lacrosse head coach.

“We’ll deal with the leadership of the program after we handle the situation and take care of each other,” he said.