HOUSTON — Many of the Houston Texans didn’t want to wait until Sunday to begin training for their season.

More than 30 players showed up at Reliant Stadium on Tuesday morning and immediately started conditioning drills and meeting with their coaches. Houston officially opens training camp Sunday, 15 days ahead of the preseason opener against the New York Jets.

“It felt really good to actually come back through these doors and have a set place to work out,” said defensive tackle Earl Mitchell, beginning his second season.

Mitchell was one of several defensive players who got their first official taste of new coordinator Wade Phillips’ 3-4 alignment, a switch from last year’s 4-3. But Mitchell, expected to play nose tackle in the defense, got a jump-start during the lockout by studying film of last year’s Cowboys, who played the 3-4 when Phillips was head coach. He also contacted Pro Bowl defensive tackle Jay Ratliff, who has started at the same position in Dallas since 2007.

“I looked at a lot of Dallas Cowboys’ film, and looked at a lot of things that Wade Phillips was looking for in this defense,” said Mitchell, a third-round draft pick in 2010. “I think I’ve got a pretty good head start on what he’s looking for.”

Defensive end J.J. Watt, Houston’s first-round pick out of Wisconsin, also studied the Cowboys’ defense. Rookies across the league missed out on valuable offseason workouts because of the lockout, so Watt was peppering coaches with questions about the scheme Tuesday.

“We all need to learn quickly,” Watt said. “As a rookie, there are a couple more things I need to learn, just about being an NFL player. But I consider myself a quick learner, and I consider myself a guy who’s going to study as hard as I can to get that defense learned, so when that first game rolls around, I’m going to be ready to go.”

The day wasn’t all about work, more like “the first day of school,” according to tight end/fullback James Casey. The Texans were barred from talking with coaches during the lockout, and they spent much of Tuesday simply reconnecting.

“A lot of talk about families and what’s been going on in our lives,” tight end Joel Dreessen said. “It was tough from a personal standpoint because, yeah, we work with these people, but they’re also our friends and colleagues. We know them, and it’s kind of weird when you’re not allowed to speak to them. It was a lot of catching up.”

The Texans will go through daily workouts and meetings leading up to Sunday, when they’re scheduled to report to camp and due for physicals. In the meantime, the team will be an active player in free agency, possibly making a major bid at Pro Bowl cornerback Nnamdi Asomugha to shore up their porous secondary.

Another priority is re-signing Pro Bowl fullback Vonta Leach, an unrestricted free agent. Ralph Vitolo, Leach’s agent, said Texans vice president of football administration Chris Olsen contacted him early Tuesday morning.

“We talked a little bit,” Vitolo said in a phone interview. “He wanted to get together and see if we couldn’t banter some numbers around, and I told him we could. There are no numbers or anything yet, we just wanted to touch base. That’s all we’ve done so far.”

Leach was the lead blocker for Arian Foster, the NFL’s leading rusher in 2010. Vitolo said Olsen told him the Texans want Leach back, but he says his client wants to test his market value after his first All-Pro season.

“We’ve just got to kick around some numbers,” Vitolo said. “We’ll just have to wait and see how that plays out.”

Casey is particularly interested in Leach’s decision, because it will determine where he’ll play. He was Houston’s third-string tight end in 2010, but also took practice reps at fullback.

“They haven’t told me anything,” Casey said. “I’m just ready to do whatever. I’m just trying to get on the field any way I can, whether it’s tight end or fullback stuff, they haven’t mentioned to me whether I’ll be doing either or. They kind of just said, just like last year, know both of them.”

Another Houston free agent is receiver/kick returner Jacoby Jones, who caught 51 passes for 562 yards in 2010, both career highs. Kennard McGuire, Jones’ agent, said in a phone interview that the Texans have contacted him as well.