SAN FRANCISCO -- The grandparents of slain Dodger fan Jonathan Denver  released a statement Friday that expressed devastation at their loss and stressed that Denver and his father were "calm, level-headed personalities and ... not the type to initiate an altercation."

Robert Sr. and Anne Marie Preece, of Covina, asked for privacy and said that "until we have some time with our son, we will not have clear details on what ensued -- only that everything went bad very quickly."

Their son, Robert Preece, and his two sons had planned Wednesday's get-together at the Giants-Dodgers game in San Francisco as a celebration of Preece's 49th birthday, they said.

It had taken a while to plan but finally came together. Preece traveled north from Alhambra, the boys south from Fort Bragg.

"They had a great time at the game sending pictures to family and friends throughout the evening," Denver's grandparents wrote, saying the group then "walked a few blocks from the stadium for a birthday drink."

San Francisco police say an altercation then ensued between Denver's group and another group of young men, one of whom was wearing a Giants cap. An initial fight ended without serious injuries, but Denver was stabbed during a second altercation that followed.

Police on Thursday booked Michael Montgomery, 21, of Lodi, into San Francisco County Jail on a charge of murder after he made incriminating statements about the late Wednesday slaying.

A distraught Montgomery told his father in a phone call that he acted in self-defense after Denver threw a chair at him, according to the Lodi News-Sentinel.

In their statement, however, Robert Sr. and Anne Marie Preece described their grandson as "a gentle, kind-hearted soul who loved his brother and his family very much ... Jon was our grandson, a son to Robert, a nephew to our five daughters, a cousin to many, and an uncle.

"Jon was always smiling, and that is how is we will forever remember him," they continued. "We feel that this incident underlines a symptom of a society whose values seem to have deteriorated over time. There is a loss of respect for human life, of family values, honesty, and of the benefit of differing opinions."

The Preeces extended gratitude for "all the kind expressions of sympathy, especially from the Stow family." (Bryan Stow, a 42-year-old paramedic, was savagely beaten outside Dodger Stadium in 2011, targeted because he was wearing Giants clothing.)

Meanwhile, Friday, North Coast Plumbing & Heating, where Denver worked as an apprentice plumber, established a memorial fund for his family. Donations can be made to the Jonathon Denver Memorial Fund, Mendo Lake Credit Union, 120 North Franklin St., Fort Bragg, CA 95437.

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Twitter @leeromney

lee.romney@latimes.com