According to a restraining order to be filed in state court Tuesday, Timothy Murphy said Steve Williams stole the historic blast from him during a melee in the left-center field bleachers at SBC Park on Sept. 17.
The suit says Murphy sat on the ball and tried to secure it with his leg before it was grabbed from him.
Williams said in an interview that he did not steal the ball but found it at the bottom of the heap of people.
"We all got in this pile. There were people everywhere," the 26-year-old from Pacifica said, adding that he did not kick or punch anybody to obtain the baseball.
Murphy could not be immediately located for comment. A message left with his San Jose attorneys Monday night was not immediately returned.
Bonds became the first new member of the 700 club in 31 years, joining Babe Ruth and Hank Aaron. He has 703 career home runs and is closing in on Ruth (714) and Aaron (755).
It's not the first time fans headed to court over the fate of a Bonds homer. In October 2001, Bonds' record-setting 73rd homer of the season sparked litigation that ended when a judge ordered both men to split the $450,000 the ball fetched.