Hammer, who has sold more than 50 million records worldwide, threw out the first pitch Sunday, and the first 15,000 fans at the Coliseum received commemorative bobblehead dolls of the recording artist -- who worked in the A's organization long before he became well known for his 1990 hit single "U Can't Touch This."
"It's very humbling," Hammer said of being honored by the club.
During the 1971-72 season, when Hammer -- who was given the moniker by former A's great Reggie Jackson -- was 11 years old, then A's owner Charles Finley spotted the young entrepreneur outside the Coliseum selling unused player tickets and offered him a job.
"Mr. Finley said, 'Oh, Hammer, you don't have to be my competition, come in and work for me," Hammer said. "He took me straight up to his box, and that began our relationship.
Hammer's two older brothers were already working for the A's, one as a bat boy and the other as a clubhouse assistant. As part of his job, the young Hammer relayed stats to the press box, and also did the play-by-play broadcast for home games.
Hammer said he used his experiences at the Coliseum as a blueprint for his successful music career.
"The years I was here were five consecutive division championships and three consecutive World Series, smallest administration staff in baseball, but profitable," he said. "It was a fine-oiled machine with enough theatrics to make it marketable and exciting for fans. I look at it very fondly."
The recording artist credits all of that to Finley and the way he ran his team -- from finding innovative in-game promotions, changing uniform colors and even spearheading the movement to have World Series games played at night. Because of that, Hammer said he believes Finley, who passed away in 1996, should be inducted into the Hall of Fame.
"You're talking about a man who would acquire talent, curate talent, market the team, promote the team and then actually win division championships and world championships," Hammer said. "Then to let you know that it was not an accident, he would do it consecutively, year in and year out.
"So yeah, he deserves to be in the Hall of Fame. He earned it."