They warned him to stay away, so when the 34-year-old German ignored their requests, he was arrested and charged following an altercation at the Wimbledon gates.
On Thursday, Albrecht Stromeyer, charged with breaching the peace and criminal damage, was ordered to put up a bond of 300 pounds ($456) to ensure that he stays away from the American tennis star for the next 13 months.
Stromeyer told police when he was arrested that he "loved" Williams "but will never hurt her."
Police said he has followed her to tournaments in Germany, Italy, Britain, France and the United States.
Stromeyer, who lives with his parents in Frankfurt, Germany, did not contest the charges when he appeared in Wimbledon Magistrates Court. He left the court from a back entrance, his head covered with a black hood without eyeholes, and made no comment.
Hours after Stromeyer appeared in court, Serena beat Amelie Mauresmo in a Wimbledon semifinal to advance to Saturday's final against her sister Venus.
Serena said after her win that she wasn't aware that Stromeyer had appeared in court until just before Venus played her semifinal match against Justine Henin.
"I don't really pay any attention to anything like that," she said. "But I don't see how it could affect my game, him being arrested. I'm a strong person. I try not to let things like that affect me."
Oracene Williams, Serena's mother, admitted that since Stromeyer wasn't arrested for stalking, so it would have been difficult to keep him in jail based on the minor offenses.
But when asked whether she wishes the man had been kept in custody, Oracene Williams replied: "I think it would make me a little more at ease."
"I just wish he would get some help," she added.
In court, prosecutor Martin Fox said "apparently Mr. Stromeyer has a fixation for tennis player Serena Williams."
"Information was received by local police to that effect. There have been previous incidents where Mr. Stromeyer tried to get close to Miss Williams in both Arizona and Rome.
"The defendant was seen and recognized by officers. Officers tried to prevent the defendant riding down the road (on a bicycle). Eventually he had to be taken off by force."
"He said: 'I don't hate her, I love her, I will never hurt her,"' Fox quoted Stromeyer as saying.
Outside the court, Metropolitan Police Chief Supt. Des Stout said police were aware Stromeyer was in the area around Wimbledon and had asked him not to come to the grounds.
"We were in touch with him beforehand and had asked him to stay away, but he didn't comply," said Stout. "He is deemed a nuisance rather than a danger, and we don't believe he is violent. His ambition would be at some stage to talk to her."
Italian police, acting on information and photos provided by Interpol, had stopped Stromeyer on May 18 at the Foro Italico complex during the Italian Open.
Rome police spokesman Antonio Del Greco says Stromeyer has a history of "harassing" Serena and has been stopped at tournaments in the United States and Germany.
Oracene Williams also reported seeing Stromeyer at a tournament in May in Berlin and at the French Open last month, where he showed up at their hotel.
In March, Stromeyer tried to visit Williams at a hotel in Scottsdale, Arizona hotel, and was later arrested for indecent exposure when he allegedly took his clothes off after a desk clerk refused to contact Williams.
A full-time bodyguard is accompanying the Williams family at Wimbledon.
In April, a man who followed Swiss tennis player Martina Hingis was sentenced to two years in prison for stalking and trespassing. Dubravko Rajcevic, a 46-year-old Croatian-born naval architect and Australian citizen, was arrested when he ignored an order from police to stay away from Hingis during a tournament at Key Biscayne, Florida.
By Dennis Passa