If not for a chance meeting, he may have never played again.
Casilla, born in the Dominican Republic, began playing in the streets of San Cristobal with friends. It was as simple as finding an open area and playing with teams according to what side of the neighborhood the kids lived on, sharing a few gloves, bats and baseballs.
One of Casilla's friends -- who played on an organized team -- told his coach about Casilla, and the coach, seeing the youngster's talents, invited him to be a part of the Little League team.
Casilla's first game didn't exactly start smoothly. He was penciled in to start at second base.
"The coach told me, 'Go to second,'" Casilla said. "So I just stand right on the bag. The shortstop said, 'No, you have to go a couple more steps to your left.' So that was funny."
As a Little Leaguer, Casilla saw Major League Baseball on television and thought of it as a virtually unattainable goal. He watched Dominican stars like Vladimir Guerrero, Ronnie Belliard and Julio Franco.
But Casilla never thought he could be like them.
"I saw that possibility kind of hard to reach," Casilla said. "I thought it was too much. I used to watch TV and I saw the stars -- but that was not in my thinking. As a kid, I was just playing for fun."
It wasn't until Casilla turned 15 that he realized what professional baseball could bring.
"Coming from a poor country, knowing it's going to give you an opportunity to support your family," he said, "that's when you really put interest into it."
Casilla continued to play and excelled. But now standing at 5-foot-9 and 180 pounds, Casilla seemed to be hampered by his lack of size, which may have cost him a chance to impress then-Angels scout Leo Perez.
"I was always one of the smaller guys, but one of the best hitters," Casilla said. "[Coach] had five or six guys that were ready to try out and sign. So when we had a scout in town, he didn't show me. I think he was afraid to because of my size."
His coach may not have shown him off, but Casilla -- who had just turned 18 -- found a way to dazzle the scout regardless. Casilla's club squared off against a team that had players from the Phillies and Marlins organizations.
Perez was walking down the stairs to the field when Casilla ripped a line drive off the center-field wall. Perez told Casilla's coach he wanted to see him hit again.
"I took eight at-bats," Casilla said. "I got six or seven hits."
The scout was even more impressed when he learned Casilla was a budding switch-hitter, though he was more advanced as a right-handed batter at the time. Perez sent Casilla to the Angels' team complex to practice with the organization's professional players on several occasions.
But as Casilla made trip after trip, he still wasn't offered a contract.
"I didn't think he was going to sign me," Casilla said. "That was so frustrating."
Heightening the frustration were Casilla's difficulties at home.
"I was just finishing high school," Casilla said. "I saw my Mom working, my Dad working. I had the same shoes every day, the same clothes every day.
"I said, 'Man, I've got to do something here.' I told my Mom, 'Hey, I've got to find a job because I'm not helping here.'"
Casilla felt he had no choice but to stop playing baseball. So for a month and a half, he did.
But one day while at the grocery store, Casilla spotted Perez.
"He came to me and said, 'Hey, man, where have you been? I've been looking for you all over the place. You have to go back and play. I'm going to sign you,'" Casilla said.
Casilla trained for a week before returning to the States again for a large tryout at the Angels' complex. The scout hesitated to sign Casilla previously because their other scouts had yet to see him play in person.
The Angels brought in about 35 infielders, 50 pitchers and 40 outfielders to run through drills and play a game. Casilla recorded two hits in three at-bats and played solid defense. He got the call later that day, which was a Friday.
"He called me and said, 'Hey, congratulations -- I'm going to sign you,'" Casilla said. "'Go to my house on Monday and we'll sign all the paperwork. Bring your Dad, your Mom, your ID.'
"Oh my God. That was a big emotion. That was one of the happiest moments in my life."
Nine years later, Casilla has carved out a niche for himself with the Twins as a utility infielder. He's hit as a well as .281 (2008) and collected as many as 21 doubles (2011). He even provided the walk-off single in 2009 that gave the Twins an American League Central title in a tiebreaker against the Tigers.
But what's most important for Casilla is returning to the Dominican in the offseason and holding tournaments for kids, providing uniforms and other necessities.
"When I was growing up, we had Jose Rijo, Raul Mondesi, Jose Guillen -- they made tournaments," Casilla said. "I remember that I had a lot of fun. Now, I feel that I have a responsibility to do it, because I lived it and I had the opportunity from those guys. They gave us a chance to play."
Casilla doesn't know where he would be today if he had never run into Perez that fateful day at the grocery store. But he does have words of advice for other kids in the Dominican who find themselves discouraged.
"Just stay positive all the time," Casilla said. "Work hard and don't stop working hard to reach your goals."
Jordan Garretson is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.