But for the first time, Walker officially can call himself a professional player.
Walker and the White Sox agreed to a $795,000 signing bonus as part of a Minor League contract announced prior to Tuesday's 5-3 loss at U.S. Cellular Field to the Royals. The White Sox made the switch-hitting outfielder their top pick and the 47th overall, taken in Compensation Round A as compensation for Arizona signing free-agent reliever J.J. Putz.
With his mother and agent in attendance, Walker made his first appearance at the ballpark where he hopes to soon be playing on a regular basis.
"It feels great," said Walker of agreeing to terms with the White Sox and getting ready to begin his career this weekend at their Advanced Rookie Great Falls affiliate. "I've been dreaming about it since I was a little kid, and finally signing and to get out and play feels good."
"He's a talented kid," said White Sox director of amateur scouting Doug Laumann. "The ability that he has to make contact and to run and play defense puts him a little ahead of the curve, because he's going to be able to contribute even if his bat struggles at times."
The 20-year-old hit .402 with 11 doubles, eight triples, four home runs, 50 RBIs and 76 runs for Central Arizona this past season. He pushed his team to the NJCAA World Series championship game, before losing on a walk-off homer to Navarro (Texas) in extra innings.
Adding a switch-hitter to the mix and a player who swiped 65 bases in 68 attempts over 63 games is an exciting proposition for the organization. Walker's speed and experience could provide boosts to his Major League quest. The White Sox took a similarly athletic outfielder in Jared Mitchell as their top pick in the 2009 First-Year Player Draft, but Mitchell missed the 2010 season due to a torn tendon in his left ankle and is hitting .225 with 101 strikeouts for Class A Winston-Salem this season.
"We're still real confident in Jared Mitchell," Laumann said. "They're similar-type players and we think they both have the chance to be center fielders, top-of-the-order guys, and that's what we're looking at for Keenyn. Now we've got two of them, so it's not a bad problem to have.
"Again, I think we'd be unrealistic to say that he can move like some of the guys we've had the last few years. But we do have the need.
"Sometimes when you're a young hitter, the hardest thing for that young hitter to do, especially when you're hitting right-handed, is handle that tough, hard slider, a pitch you don't see a lot in college or in high school. That adjustment for him doesn't really exist because of being a switch-hitter -- he's hitting from the left side, so he doesn't really have the difficulty with that pitch."
Before coming to terms with the White Sox, Walker was playing in a wooden-bat, summer-collegiate league in Alaska. Walker said he "freaked out a little bit" by the sun never going down, but otherwise enjoyed his time.
Montana is his next destination, after his brief Chicago stop for Tuesday's physical and introduction and a return home to Utah to pack. Walker was drafted by the Cubs in the 16th round of the 2009 First-Year Player Draft and drafted in the 38th round by the Phillies in the 2010 Draft.
He felt as if the time was right with the White Sox in 2011.
"I felt ready," Walker said. "The first two years I thought I was ready, but I wasn't. I had a great season this season, and mentally and physically I thought I was ready to start my pro career.
"Hopefully, I develop more as a power guy, shoot it gap to gap. I can add my speed, and other than that, just play ball."