"I know that it's a big year for me," Antonelli said. "Last year, I played in 50 games and was hurt. The year before that, I didn't play well. You cannot play the way I have played forever or you won't be playing baseball. I know that."
This much, Antonelli is sure of. As for what has happened the last two years, where his swing betrayed him, his batting average plummeted and his confidence sank, the second baseman still isn't quite so sure how to explain it.
A first-round pick of the Padres in 2006 (17th overall), Antonelli's stock has slipped the last two seasons. After hitting .298 in his first two professional seasons, Antonelli has a .199 batting average -- and a lot of questions -- to show for his last two seasons.
"In college, I was a pretty good hitter, and to go from that to a bad hitter was really weird," Antonelli said. "It's frustrating when you can't hit anymore. I just want to do it because I know I can hit. I'm sick of having bad years. That takes the fun out of baseball."
Antonelli has reason to think he might be on the cusp of pulling out of a two-year funk at the plate, which is why he showed up in Peoria a week before the rest of position players, to continue work on the swing he rebuilt last fall.
"The last two years has been a lot of tweaking. I got into a lot of horrible habits and I couldn't get out of them," Antonelli said. "I didn't even really know what I was trying to get out of. I just knew my swing wasn't working. It was two years of experimentation."
Antonelli's problems started in 2008, when he hit .215 with Triple-A Portland. He wasn't so much overmatched (86 strikeouts in 451 at-bats), but at times, it was all he could do to get the ball out of the infield.
Last year in Spring Training, Antonelli suffered an injury to his right leg. The injury wasn't considered serious at first, but the pain lingered and kept Antonelli from playing at times. After a series of cortisone shots, he was eventually told he had an injury to his tib-fib joint, which is located between the tibia and fibia. The injury required rest.
The injury kept Antonelli, who was set to play for Portland again, in Arizona longer than he had hoped. He didn't play his first game in Portland until May 12. He struggled again, hitting .196 in 59 games with the Beavers before heading back to Arizona, this time to essentially rebuild his swing from scratch.
"During the year, it was hard because I was getting ready to play," Antonelli said. "When the season was over, I came to Arizona and just hit for two weeks with no games. Then we had a five-week period where I could work on stuff and take it into games. ... Something clicked during that time."
Antonelli worked closely with Padres Minor League hitting coordinator Tony Muser on his swing. The time was beneficial, as Muser watched him swing the bat for an extended period of time.
Finally, a flaw in Antonelli's swing was detected.
"I got into the horrible habit of swinging with my shoulders and pulling off the ball," Antonelli said. "I would yank off the ball, my shoulder would come out and when it happens, your bat doesn't stay on the right plane of the plate.
"I didn't know that. I was just swinging. I couldn't stop doing it. I would hit ground balls to third base. I didn't have any power anymore because I couldn't get any backspin carry on the ball."
Muser said Thursday that he's encouraged that the things he and Antonelli worked on in the fall have carried over to the spring, though he cautioned that fixing a mechanical flaw is just one part of the equation.
"He's got a base underneath him now," Muser said. "A big thing for me is it's going to be as much mental as it is physical. He's coming off two pretty two tough years. He wants it so bad. He's going to have to relax and let his natural ability take over."
For now, Antonelli will continue to work this spring on hitting the ball the other way to right field, something he and Muser worked on to get his bat where it needs to be in the hitting zone.
It's a minor tweak Antonelli hopes will lead to bigger things offensively this season and let him get his career back on track.
"I think I'm going to do well. I feel a lot better than the last few years," Antonelli said. "I think I've broken a lot of bad habits."
Corey Brock is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.