Packers rookie Mike Pennel, shown sacking Rams quarterback Shaun Hill on Saturday, has been a pleasant surprise. Credit: Associated Press

Green Bay — The success or failure of the Green Bay Packers on defense this season largely will depend on how they stop the run, something the team hasn't done extremely well since 2009 and generally has been average to poor ever since.

The early returns on the downsizing of the defensive line have been positive, for the most part. Wide bodies Ryan Pickett, Johnny Jolly and C.J. Wilson are gone, but their smaller replacements have been holding up.

On Saturday, the St. Louis Rams mustered only 6 yards in six carries when their starters were matched against the Packers' starters.

"They're very stout up front," Rams coach Jeff Fisher said. "It was a little frustrating at times just because of the penetration. There was so much penetration."

St. Louis had a 100-yard rusher in five of the last nine games last season. Top returning rushers Zac Stacy and Benny Cunningham didn't have much luck against the Packers, but part of the problem was the absence of left tackle Jake Long (knee) and right guard Rodger Saffold (unknown).

Inside linebackers A.J. Hawk and Brad Jones were on top of their games in two-series stints. Hawk was attacking, not catching.

Having the bulk of Julius Peppers (6 foot 6, 285 pounds) at outside linebacker rather than Nick Perry, Mike Neal, Andy Mulumba and Nate Palmer, who all played the position last year, also has been noticeable against the run.

Throughout three weeks of practice and two exhibition games, the defensive line in the 3-4 base has featured Datone Jones at left end, B.J. Raji at nose tackle and Mike Daniels at right end.

Compared to the departed behemoths, Jones (6-4, 285) is light and Daniels (6-0½, 303) is short.

Starting with opening night on Sept. 4 against Marshawn Lynch and the Seattle Seahawks, the Packers will begin finding out if their new front three can hold the fort.

Daniels is the club's premier defensive lineman. Strong and quick, determined and domineering, he might be as indispensable as anyone on defense.

Had this been five years ago, or before Roger Goodell made it almost a cardinal sin to breathe on quarterbacks, Daniels probably would have had three knockdowns of Sam Bradford in his 19 snaps. As it was, Daniels beat backup Mike Person but then pulled up to avoid a fine.

Tackle-guard Greg Robinson (6-5, 332), the second pick in the 2014 draft, moved Daniels three times on running plays. However, Daniels shed Robinson and tackled Stacy for a loss before disengaging from center Scott Wells and assisting on another tackle.

Based on what we've seen, the expectation is that Daniels will be less vulnerable to the run than Jones.

Jones has made gains restructuring his body. He is strong, and he does play hard. Plus, he is confident in his run-stop ability.

Through 44 snaps, however, Jones basically hasn't made a play. He has been OK at the point of attack.

"I'm a defensive end, not a D-tackle," Jones said last week. "I'll put my height and weight up against any defensive end. You didn't see me on the ground one time (against Tennessee). Not one time."

If the Packers need more ballast, Josh Boyd (6-2½, 309) clearly is a better option than rookie Khyri Thornton (6-2 ½, 308).

Although they are almost mirror images of one another on the hoof, Boyd is more explosive, combative and aware. He's quicker off the ball, more of a pass-rush threat and has shown the capability of playing across the line of scrimmage.

It wasn't until the Rams inserted their No. 3 offense that Thornton made his first play or two of the exhibition season. A third-round pick, he's basically occupying space as he learns the ropes.

The Packers viewed former Viking Letroy Guion (6-3½, 315) not only as Raji's backup but also as a rotational player at end. But unless he is back this week from a lost month because of a bad hamstring, the Packers probably can't count on him in Seattle.

If Thornton has been a disappointment for the run defense, rookie Mike Pennel (6-4, 331) has been a pleasant surprise. For the second straight game he was in the opponent's backfield, including on a sack that was set up by Mike Neal.

Of course he was working against backups, but Pennel still had six positive grades in 19 snaps in St. Louis. He's massive, moves well and keeps beating people. Most 3-4 teams would want someone like that.

As for Raji, talent has never been the issue. Little can be gleaned from his two-game, 23-snap exposure. He'll have to turn it up.

The Barclay dilemma: Before Don Barclay blew out his knee, the Packers had the offensive line covered. Now, they might not.

As dependable as Derek Sherrod looked in Tennessee, he was equally as unreliable in St. Louis.

The fear for the coaches is Sherrod held up well against Tennessee's Akeem Ayers mainly because of a grass field made even slower by a rainstorm. They'll play a lot more games on FieldTurf and in domes, the setting for his rough performance Saturday.

A week ago, some might have been wondering if Sherrod, a first-round pick in 2011, eventually could challenge David Bakhtiari, a fourth-round pick in '13.

Bakhtiari played 24 snaps against the Rams. At least 20 were against Robert Quinn, perhaps the hottest rusher in the business.

Quinn didn't have a sack or a pressure. He beat Bakhtiari inside once but the ball was gone. He also stuffed him on a third-and-1 running play.

Otherwise, Bakhtiari was in almost complete control. His ability to move his feet and place his hands prevented Quinn from turning the corner, and his newfound strength enabled him to anchor against power rushes.

After watching what backups Eugene Sims and Michael Sam did to Sherrod, can you just imagine a Quinn-Sherrod matchup?

In 29 snaps at left tackle, Sherrod yielded knockdowns in 2.7 and 2.3 seconds to Sims off the edge, missed Sims a third time, failed on a back-side cut and was penalized for a false start.

In 11 snaps at right tackle, Sherrod missed Sam to abort a pass leading to Matt Flynn's scramble and was partially at fault for a sack by Sam in which Flynn held the ball 4.2 seconds.

Sherrod's feet were slow. His hand placement was off. He lunged and ducked his head.

Aaron Adams, who alternated 46 snaps between the two tackles, was overwhelmed by rookie Ethan Westbrooks, a free agent from West Texas A&M, before getting beat inside by Sam on a rush that turned into a sack.

Buoyed by his top-flight performances against defensive end Chris Long in 2011 and '12, Bryan Bulaga played 24 snaps against Long without a blemish.

It goes without saying that the Packers can ill afford to lose Bulaga or Bakhtiari.

Department of the interior: The news for the Packers at center and guard was better.

For the second Saturday in a row, center JC Tretter was outstanding. On the first drive, he made a difficult reach block against rookie three-technique Aaron Donald, the 13th overall selection, look easy as Eddie Lacy chugged on by for a 7-yard gain.

Tretter played with power and bend, blocked crisply at the second level, was consistent in protection and didn't appear to make any mistakes.

Rookie Corey Linsley, the backup center, drew a pair of penalties, one of which wiped out a touchdown.

He also pancaked defensive tackle Deantre Harlan on a 9-yard rush by DuJuan Harris, moved easily on a pair of screens and generally stayed between his man and the ball.

Meanwhile, Lane Taylor solidified his hold on the No. 3 guard job with a steady 40-snap showing.

Taylor was much better at right guard, his home for most of the summer. In 29 snaps, he might have had two minuses. In 11 snaps later at left guard, he left early on a combination block that resulted in one of Linsley's penalties and gave up his only pressure.

Taylor (6-3, 324) is similar in size to Josh Sitton and T.J. Lang. He also exhibits a nasty streak and tries to finish blocks, just as the regulars do.

Linsley (6-2½, 301) doesn't have Taylor's bulk but is the better athlete.

If Taylor, Linsley and Sherrod are the three backups on the 53-man roster, the coaches will have to decide if Taylor or Linsley is the first sub at guard. Linsley backed up at guard and tackle at Ohio State in 2010-'11 but has been a center only in Green Bay.

Making sense: To gauge outside linebacker Jayrone Elliott, you need to know something about the right tackle that he devoured for three sacks in the span of seven plays late in the fourth quarter.

Sean Hooey (6-8, 304) started six of 27 games at the University of Cincinnati before joining the Rams as a free agent in 2013. He spent all last season on their practice squad.

Besides ideal height, Hooey has nice arm length (34¼ inches), small hands (93/8), a 5.37-second 40-yard dash and upper-body weakness (just 16 reps on the bench press).

Hooey, who also had some snaps against Andy Mulumba, was beat outside by Elliott for sacks in 2.8, 2.7 and 2.1 seconds. On the final sack, Elliott anticipated the snap count to the nth degree.

Actually, I've seen more oafish tackles than Hooey in exhibition games over the years. Elliott has done his share of damage on the Packers' practice field, too.

About a dozen teams had scouts at the game. After seeing Elliott's exploits, it's almost a given that a 3-4 team would enter a claim if the Packers released him.

Adrian Hubbard also had a seven-play crack at Hooey. In the stretch of three plays, he had a sack (2.7 seconds) and two pressures.

Carl Bradford played 11 snaps on the left side, settling for one pressure on an inside stunt.

Mulumba, in just 15 snaps, beat blockers on four running plays and made three tackles near the line.

Tough blow: Richard Rodgers started and went the distance on the 12-play opening touchdown drive.

For the second straight week, however, the most impressive tight end was Brandon Bostick, even though his day ended after four snaps because of a lower-leg injury.

On his first play, Bostick released more quickly off the line and into a route than either Rodgers (17 snaps) or Andrew Quarless (26) can do.

On his second play, Bostick moved from his position in the backfield and smothered a spin move by blitzing Jo-Lonn Dunbar, a physical linebacker.

On his third play, Bostick made a tough catch of a bang-bang pass in the seam for 9 yards knowing he would be drilled by the safety (T.J. McDonald) and probably the linebacker (Dunbar).

The injury appeared to occur on that tackle. He coasted through a fourth play before leaving.

Rodgers' blocking was inconsistent. Quarless played exactly the way he did last year.

The Packers can only hope Bostick will be back soon.