With 5.5 sacks for the season, all of them over the last three games, San Francisco 49ers rookie Aldon Smith is on pace to finish the regular season with 14.5.

That would tie the sack-era NFL rookie record Jevon Kearse set in 1999. Sacks became an official stat in 1982.

Mel Kiper Jr. expected Smith to make an immediate impact despite facing a transition to the 3-4 defense. Smith is doing more than making an impact. He's turning into a candidate for defensive rookie of the year.

The Washington Redskins' Ryan Kerrigan is another prominent candidate. He has two sacks, three passes defensed, two forced fumbles, one interception and a touchdown. Denver's Von Miller has five sacks and also could factor, although the Broncos reduced his role recently.

Smith ranks fifth in the NFL in sacks and first among rookies. He also has a safety.

Veteran Parys Haralson remained the 49ers' starting outside linebacker for San Francisco against Detroit in Week 6. But the Lions' pass-oriented offense led to more snaps for Smith and the 49ers' nickel defense. The same was true when San Francisco faced Philadelphia in Week 4.

The chart, provided by ESPN Stats & Information, shows game-by-game snap counts for the 49ers' linebackers this season. Smith played a season-high 62 snaps against the Lions.

2011 San Francisco 49ers LB Snap Counts