He was 16 years old then. Before long, he was throwing so well from behind the plate that the Dodgers decided to try him throwing from in front of the plate.
Diaz became a pitcher.
The change came in 2001 in the Pioneer League. Diaz threw out 45 percent of aspiring basestealers. He led the league's catchers in putouts and assists. He even played some at first base and at third.
"I was in rookie ball at Great Falls and the manager, Sly Silvestri, said, 'You want to pitch for fun? Go to the bullpen and see if you like it.'"
Well, Diaz liked it and a new career was born. Now, after throwing the baseball from 60 feet 6 inches for more than five years, he's on the Royals' roster for his Major League debut.
He joins the contingent from the Dominican Republic, guys he knows from winter ball and from the Minors. Diaz is from San Pedro de Macoris.
Diaz was obtained from the Texas Rangers in the trade for veteran slugger Matt Stairs. Before the July 31 deal, Diaz had a 2-0 record with four saves and a 2.40 ERA in 36 outings combined from Double-A Frisco and Triple-A Oklahoma.
The Royals sent him to Triple-A Omaha where he was 2-3 with a 5.40 ERA in 13 games as a reliever.
Diaz has a 95-mph fastball, a sharp-breaking curveball and a changeup.
"Check his stats. His biggest problem, like anybody, is his command," Omaha pitching coach Tom Burgmeier said.
OK, in a total 82 innings this season in the minors, Diaz walked 57. But he also had 91 strikeouts.
"He's like [Joel] Peralta," Burgmeier said. "Give me the ball and let's go. It's like the gunslinger mentality and that's good. You can't teach that."
Diaz, a 6-0, 240-pound right-hander, has been around. The Royals are his sixth organization.
"You go up and down," he said. "You find a way when you're down to go back up again."
Wood working: Right-hander Mike Wood joined Diaz and catcher Paul Phillips in reporting from Omaha.
Wood, rehabbing from back inflammation, was 0-2 with a 6.41 ERA for Wichita and Omaha. Before his injury, he was 3-2 with a 5.66 ERA in 21 games for the Royals.
In his final start, Wood lost Monday to Iowa, 4-3. He went five innings and gave up two home runs. The Royals will use him in relief.
Minor details: Class A High Desert made the California League playoffs as a wild-card entry. ... Class A Burlington finished the second half 28-41, sixth in the Midwest League's West.
Up next: The Royals end their homestand against the New York Yankees at 7:10 p.m. CT on Wednesday. The Yankees will send left-hander Randy Johnson (15-10, 4.94 ERA), against right-hander Runelvys Hernandez (5-8, 6.31 ERA).
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.