Stanley Kirk Burrell was born in Oakland, California, on March 30, 1962.^[38] His father was a professional poker player and gambling casino manager (at Oaks Card Club's cardroom), as well as a warehouse supervisor.^[39] He grew up poor with his mother (a secretary), and eight siblings in a small apartment in East Oakland. He recalled that six children were crammed into a three-bedroom housing project apartment. The Burrells would frequent thoroughbred horse races, eventually becoming owners and winners of several graded stakes.^[39]

In the Oakland Coliseum parking lot the young Burrell would sell stray baseballs and dance accompanied by a beatboxer. Oakland Athleticsteam owner Charlie Finley saw the 11-year-old doing splits and hired him as a clubhouse assistant and batboy as a result of his energy and flair.^[7][40] Burrell served as a "batboy" with the team from 1973 to 1980. In 2010, Hammer discussed his lifelong involvement with athletes on ESPN's First Take as well as explained that his brother Louis Burrell Jr. (who would later become Hammer's business manager)^[41][42] was actually the batboy while his job was to take calls and do "play-by-plays" for the A's absentee owner during every summer game.^[43] The colorful Finley, who lived in Chicago,^[7] used the child as his "eyes and ears".^[44] Reggie Jackson, in describing Burrell's role for Finley, took credit for his nickname:

Hell, our chief executive, the guy that ran our team, uh, that communicated [with] Charlie Finley, the top man there, was a 13-year-old kid. I nicknamed him "Hammer" because he looked like Hank Aaron [whose nickname was "The Hammer"].^[44]

Team players, including Milwaukee Brewerssecond baseman Pedro García, also dubbed Burrell "Little Hammer" due to his resemblance to Aaron.^[7][39] Ron Bergman, at the time an Oakland Tribune writer who covered the A's, recalled that: He was an informant in the clubhouse, an informant for Charlie, and he got the nickname "Pipeline".^[44] According to Hammer:

Charlie said, "I'm getting you a new hat. I don't want you to have a hat that says "A's" on it. I'm getting you a hat that says 'Ex VP,' that says 'Executive Vice President.' You're running the joint around here." ... Every time I come down to the clubhouse, you know, Rollie would yell out "Oh, everybody be quiet! Here comes Pipeline!"^[44]

He acquired the nickname "MC" for being a "master of ceremonies" which he used when he began performing at various clubs while on the road with the A's, and eventually in the military.^[7]Hammer, who played second base in high school, dreamed of being a professional baseball player but did not make the final cut at a San Francisco Giants tryout.^[7] However, he has been a participant/player in the annual Taco Bell All-Star Legends and Celebrity Softball Game wearing an A's cap to represent Oakland (American League).^[45][46][47]