SANTA CLARA – Wide receiver Michael Crabtree missed his second straight practice Sunday after going down with a lower leg injury late in Friday's session.

The 49ers, as is their habit when it comes to injuries, declined to get into specifics, but general manager Trent Baalke said it had nothing to do with the broken foot Crabtree suffered as a rookie in 2009 and again last season.

Late in the practice, Crabtree walked from the locker room to the field with strength and conditioning coach Mark Uyeyama. He moved without a limp and had black tape on his right calf.

Crabtree most recently broke his left foot in June 2011 during a player-organized workout at San Jose State. That caused him to miss training camp and the exhibition season, and he was not fully healthy when the regular season began.

Crabtree has not played in a preseason game since the 49ers drafted him 10th overall in 2009. But Baalke indicated that the receiver's current injury is not as serious as the previous ones.

"He's working hard at it (rehabilitating), and the progress looks good," Baalke said.

Hard hitting – The team donned pads and allowed true contact for the first time this offseason. Jim Harbaugh referred to it as "thudball," and it was an apt description.

The hard hitting including two knockdowns by defensive end Justin Smith, who sent offensive linemen Derek Hall and Daniel Kilgore sprawling onto their backsides on separate plays.

On offense, tight end Delanie Walker seemed to have fun blocking linebackers and defensive backs on a couple of running plays.

"The guys up front really get a lot of work mentally over the course of the offseason. But to simulate playing low, playing hard, playing aggressive … pads are required," Jim Harbaugh said. 'So, that'll be the first thing we're going to really stress and focus on with these guys is getting them to play lower pad level coming off the offseason."

Rookie ejected – Rookie receiver Brian Tyms was dismissed from practice after he threw down fellow rookie Trenton Robinson on punt coverage. While there was contact, Harbaugh didn't want players taken to the ground. Tyms and Harbaugh had a long talk after the practice.

Injuries – Wide receiver Joe Hastings appeared to injure his upper leg and sat out practice. Linebacker Tavares Gooden (illness) did not take part in practice.

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