Impressions gathered from viewing 24 of 26 training camp practices over the course of 21 days:

– Not long after camp opened, Lane Kiffin offered a preemptive strike, musing about the importance of the offseason program in light of the fact that his two best players weren’t even participants.

Cornerback Nnamdi Asomugha walked into camp on time, signed his exclusive free agent tender and was so good he looked like a bargain at $9.7 million.

Defensive end Derrick Burgess put on eight to 10 pounds of muscle working out on his own, showing up only to the mandatory minicamp, and was essentially unblockable. Raiders tackles found themselves getting nothing but air or simply being shoved aside by one of Burgess’ perfectly sculpted arms.

Defensive coordinator Rob Ryan is flopping sides with Burgess now and then, moving him from his more familiar left side to the right. The idea is to get him an a single blocker from time to time, rather than the double-team plus a chip treatment he has received so often the last two years.

The truth about training camp defense is it is can be extremely deceiving because there is no actual tackling. Tackling only happens to be the most important thing about defense.

But there was no mistaking what Asomugha brought to pass coverage and Burgess brought to the pass rush. If health is not an issue, and Asomugha’s sore foot is at least a little troubling, the Raiders have two cornerstone defensive players to help build a viable defense.

– Training camp restrictions being what they are, there is no way to know for sure if the Raiders have repaired the gaping hole in the middle of their defense which opposing runners ran through repeatedly in 2007.

They should be better, but how much better? Do they go from giving up an embarrassing 4.8 yards per carry to the 4.0 range, or could they actually do even better and be above average.

Two reasons for optimism _ Tommy Kelly’s brief but dominating appearance against the San Francisco 49ers, and the presence of Gibril Wilson at strong safety.

Kelly has a ways to go in terms of conditioning, as witnessed by his feeble yet comic attempt at taking a lap the other night after being called for offsides. Kelly was collapsing the 49ers line almost single-handedly, but to do that for four quarters he will need more stamina. Rehab from knee surgery put him behind, and Kelly needs to catch up.

The Raiders aren’t paying him all that money to be a part time player.

Wilson has been a guy who plays bigger than the 210 pounds or so he weighs, and his presence in the box will be a welcome one in a division featuring LaDainian Tomlinson, Larry Johnson and whoever is the Broncos runner of the week.

– More optimism regarding the run defense _ linebacker Thomas Howard looks a little bigger and a little meaner without sacrificing the speed and ability that makes him one of the NFL’s best pass coverage linebackers. He and Kirk Morrison are intent on shedding their reputation as pass defenders who give ground against the run.

They need to be much, much better than a year ago. The two or three series they play against a hard-nosed Tennessee running game will be a good litmus test.

– The Raiders brought a lot of pressure during training camp, which makes aggressive amateur defensive coordinators salivate with the possibility of more blitzing.

Much of the additional pressure was to prepare JaMarcus Russell for what the Raiders think he’ll see. Kiffin could have been sandbagging, but more likely he was telling it like it is the other day when he was addressing Stanford Routt’s role as a nickel back and said, “We’re not very complicated on third down, our defense. We don’t blitz very much so he doesn’t have to do very much.”

– The play of Raiders’ offensive tackles makes it a tough call, but there may be some help for Burgess in terms of a natural rush. Jay Richardson, a decent point-of-attack player as a rookie and tall enough to take away passing lanes, has had some success getting deeper into the backfield. Kalimba Edwards has practices where it looks as if he will fit nicely into the Chris Clemons role as a situational rusher.

– The resurrection of Terdell Sands to be the kind of inside force he was as a part-time player in 2006 is still far from complete. Sands conceded he went into an understandable funk last year after the death of his mother and let his weight get out of control.

He is lighter this year _ how much, no one will say _ but he has already had a knee drained and is missing practices. It’s tough to get into shape that way. Sands will probably continue to back up Gerard Warren, who through most of his career has been either impressive or invisible _ sometimes from one week to the next.

– In early practices, sixth-round pick Trevor Scott looked like he might be a wasted pick. Later, he looked like he might be a find. Line coach Keith Millard beams like a proud papa when Scott’s progress is the topic.

Yet you see Scott in person and it’s almost alarming. He physically resembles Stuart Schweigert, and in fact doesn’t look much bigger. Listed at 255, Scott, in truth, is slightly under 250. He won’t be 260 until next year at the earliest.

– When camp started, Michael Huff looked liberated to be at free safety and making the occasional play with the kind of anticipation the position requires. The plays became more infrequent as time went on.

It’s nearing make-or-break time for Huff to justify his No. 7 overall selection in 2006, and it’s a tossup as to which way it will go.

– The whole strong side linebacker issue makes for interesting reading, being that it’s a starting position and all, but the truth is the winner will be the first player off the field when its time for nickels and dimes.

That’s why the Raiders didn’t make a serious run at Takeo Spikes, who wound up in San Francisco. They’d rather pay the veteran’s minimum for an Adam Archuleta than invest another half-million or so into a player who would be an ideal strong side linebacker but spend too much time on the sidelines to justify the money.

Not saying it’s right, and in fact it probably isn’t in this case.

– DeAngelo Hall is going to catch some heat, both from opposing quarterbacks as well as the home fans. Teams are still going to avoid Asomugha, and Hall will be there for the taking. He will also occasionally make a break on the ball and make a big play, and has a knack for being in the area when balls are deflected.

If you’re expecting a shutdown corner, guess again. There are precious few of those around.

– Routt has had an excellent training camp. He could have been miffed by Hall’s acquisition but instead has appeared to elevate his performance in practice.

Now it has to carry over into games. One of Hall’s strengths is he forgets when he just got beat and it doesn’t prevent him from coming back to make a play. Routt has had a habit of letting the failures which come with the territory affect him for the rest of the game.

Routt will need to be at the top of his game, because things get extremely thin after that at cornerback.

– Bad break for Tyvon Branch, with his right thumb encased in a cast. He could still end up being a defensive contributor at some point during the season, if his goal line hit against the 49ers’ Cam Colvin is any indication.