MESA, Ariz. - The Oakland A's added a new coach to their roster on Saturday. Might've heard of him -- Jim Harbaugh.

The former coach of the San Francisco 49ers and new coach at Michigan appeared in full uniform Saturday, including high socks, for the A's. He coached first base for several innings against the Los Angeles Angels at HoHoKam Stadium.

Harbaugh wore No. 4, the number he used while playing in the NFL. He grew up in Palo Alto, California, and played on the same American Legion team as A's manager Bob Melvin, although it was a few years after Melvin.

"Let's play two, as Ernie Banks would say," Harbaugh said outside the A's dugout during pregame warmups.

They resumed their relationship after Melvin became A's manager in 2011. Harbaugh invited Melvin onto the 49ers sideline for several NFL games.

"He's an inspiration just walking out here. He's got that air about him," Melvin said. "Jim has got that work ethic. After he left the 49ers, he was in Michigan the next day recruiting. We asked him if he would (join the A's) and he talked his wife into coming out."

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Harbaugh spoke to Melvin's players briefly before they took the field.

"He's a very good speaker to his teams. I stole a bit of his material from time to time," said Melvin, who added that Harbaugh requested the high socks.

Harbaugh was a pitcher, shortstop and catcher in youth leagues, and said he felt he did the best as a catcher. He called himself a "mediocre" hitter and watched a video from former hitting guru Charlie Lau, "but I couldn't get the ball out of the infield."

Harbaugh said his father had a friendship with former Detroit Tigers pinch-hitter Gates Brown. Jack Harbaugh, a longtime football coach, and Brown grew up in Crestline, Ohio. Brown died in 2013.

"My first experience with the major leagues was going into the Detroit Tigers clubhouse and then going for a hamburger afterward. I got to see guys like Al Kaline, Ed Brinkman, Lou Whitaker. I was like 8, 9, 10, 11, 12 when I went," said the 51-year-old Harbaugh.