Decker, considered one of the top prospects in the San Diego Padres farm system, had a big first full-season campaign in 2009 with Class A Fort Wayne. He hit .299 and had 16 home runs, 64 RBIs and a .442 on-base percentage.
Decker has been named one of MLB.com's Top 50 Prospects for the 2010 season, coming in at No. 50.
Not bad for a player who won't turn 20 until February and played against foes who were two or three years older than him.
"I think that Jaff might have been the youngest guy in the league," said Mike Wickham, the Padres' director of Minor League operations. "His approach, though, is as good, if not better, than guys 2-3 years older than him."
The TinCaps, despite several player promotions, won the Midwest League championship.
The TinCaps were the 2009 MiLBY winner for Overall and Class A Team of the Year. The Midwest League affiliate for the San Diego Padres won a grand total of 101 games, including the playoffs.
But they did it in just 149 games for a .678 winning percentage en route to winning the Midwest League title.
This was a club that liked to get off to fast starts. Fort Wayne began the season 10-0. Then, in the second half, the TinCaps broke out to a 14-1 start, including another 10-game winning streak.
"It was one of the greatest baseball experiences I've ever had," Decker said. "A bunch of great guys ... we had speed, power, played great defense and had great pitching. To win it and share that with those guys, it was one of the greatest accomplishments I had."
Wickham said Decker will begin the season at Class A Lake Elsinore of the California League where he'll again be one of the youngest players in the league. As for what the Padres want to see from him in 2010, it's mostly more of the same.
"Hitting lefties, but we feel that is something that will come with experience," Wickham said. "He'll get it. We would like to see him continue to use the whole field and not get into pull-mode.
"He'll get it. He's got a real polished approach. That's what we're trying to teach."
Decker has done plenty of hitting since signing with the Padres in 2008. He hit .343 in two stops his first season in 169 at-bats.
Corey Brock is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.