Probably got mugged by the grandkids of his old friends from the Symbionese Liberation Army.
Bill Walton was a supporter of that Patty Heast crime wave way back when? Patty became a Gun Moll under a different name.
Walton and another face-left athlete were part of the SLA underground support network for leftist terrorists. He reportedly hid Patty Hearst and possibly another radical at a farmhouse in Pennsylvania.
I believe he refused to cooperate with the investigations into this MARXIST underground railroad. Never jailed for this despite evidence showing that he was present at the barn/farmhouse where Hearst hid for a while.