The most telling image about Navy SEAL Michael Murphy in the new documentary “Murph: The Protector” is a snippet of video from a high school football game.

Murphy has just caught a pass near the other team’s goal line. He’s being tackled, but it’s not obvious that he’ll go down. But he has the presence of mind and the unselfishness to lateral the ball to a teammate, who then prances into the end zone.

That is very much the picture of Murphy that emerges in this documentary, which relies on the warm memories of family, friends and Navy colleagues to etch a portrait of a true American hero.

He was “the sweetest kid,” “a great swimmer,” always looking out for others, sticking up for the bullied, a team player in everything he ever attempted.

Filmmaker Scott Mactavish uses home movies, interviews, snippets of Navy SEAL training videos and news footage to recall a life cut short by a sense of duty. Murphy was one of those killed in Afghanistan during Operation Red Wings, a SEAL mission in Afghanistan that went wrong on the ground, and was compounded by the crash of a rescue mission helicopter, leading to the worst day in the history of this “elite of the elite” commando unit.

Holden Caulfield, the antihero of J.D. Salinger’s most famous novel, longed to be a “catcher in the rye,” an everyday hero who saves children about to go over the cliff to their doom. Michael Murphy, from the way people describe him, actually did just that.

He went to Penn State and was headed toward a career in the law, like his father. But the SEALs held an allure he couldn’t resist. He embraced their fanatical training regimen as he prepared to join up and risked his Vietnam-veteran father’s wrath by doing it. He passed muster, became an officer, and when the chips were down, the character that friends and family recognized at an early age showed through.

Mactavish spends much of the movie serving up saintly banalities about this flesh-and-blood man. He wasn’t famous, like Pat Tilman, who also earned a documentary about his life and death, so the portrait of his life is necessarily limited to those who loved him. Conspicuous by her absence is his fianc?But mother Maureen and father Daniel paint a reasonably complete, polished and limited portrait.

Where the film is on surer footing is in recreating the last days of Murphy’s too-short life, the memories he left behind and the tributes that have poured in on him in the years since. It’s the emotional heart of the film and can be wrenching as we recall, with Maureen, a mother’s uncertainty when the phrase “missing in action” is given her.

But we remember, even if the film doesn’t revisit it, that early moment on the gridiron when “Murph: The Protector” showed his character, as a teenager. And we’re reminded not just of sacrifice, but of those to whom service is a genuine calling and what that bandied-about word “hero” really means.