Seahawks vs. 49ers: 5 San Francisco storylines to watch in Week 15

The San Francisco 49ers have another chance to play spoiler, this time in Week 15 as the playoff-hopeful Seattle Seahawks come to town looking to continue their elongated win streak over their NFC West division rivals.

The last time the San Francisco 49ers beat the Seattle Seahawks was back in December of 2013 -- a time when a Niners-Hawks game was must-watch television. Since then, the 49ers have fallen on hard times while, at 8-5, Seattle is a mere one win away from securing a playoff berth again.

Two weeks ago, the Seahawks drubbed the Niners 43-16 in a completely lopsided game at CenturyLink Field in Seattle. The quick turnaround is interesting, yet another loss would mean the 49ers and their fans will have to endure yet another year of hearing about that losing streak.

"It's something that's not going to go away until we win," head coach Kyle Shanahan told reporters earlier this week. "We're not going to have that opportunity to do that again after Sunday for another year. I'm glad we have another opportunity and hopefully we don't have to hear that after this weekend."

San Francisco isn't going to the playoffs. But at 3-10, fresh off a postseason-spoiling victory over the Denver Broncos last week, the 49ers can embrace the spoiler role once more with Seattle in town and hope to throw some difficulty into its playoff seeding.

Oh, and ending that losing streak would be nice too.

Here are some pointers and notes to watch for Sunday's contest.

Arik Armstead and the 49ers Run Defense

In an age where passing offense dominates, the Seahawks have found success on the ground, leading the NFL with an astounding 2,000 yards rushing and averaging a league seventh-best 4.7 yards per carry. Back in Week 13, the Hawks gashed the 49ers for 168 rush yards, and San Francisco's defense never truly found an answer to stop the run.

Coming off a week during which the Niners bottled up Broncos top running back Phillip Lindsay, holding him to just 2.1 yards per carry on 14 attempts, the team should feel pretty good about replicating those kinds of efforts.

Chief among the 49ers run stoppers is defensive tackle Arik Armstead who, as 49ers Webzone's Bret Rumbeck pointed out, is quietly putting together a very nice season.

Shanahan agreed, saying:

The main thing I like to look for is, are you getting better or are you getting worse? I've seen someone that we've been here for two years with him, we've moved him in some different positions, and I see a guy who is only getting better. If that continues, I think his expectations of things should naturally take care of itself because he has that ability.

Despite what happened in Seattle back in Week 13, the Niners are still allowing just 4.1 yards per rush -- 10th best in the NFL.

Getting the 49ers' Own Running Game Going

Seattle's defense has been stingy this season, ranking sixth best in scoring and only having given up 266 points on the year.

That said, it isn't as if head coach Pete Carroll boasts an elite run defense. To date, the Seahawks are allowing an average of 5.0 yards per carry, which ranks 29th in the NFL. Granted, when the 49ers came to town in Week 13, the Hawks were ranked dead last in this same category. So, perhaps, they've improved moderately in recent weeks. But it doesn't change the fact it's a weakness for Seattle.

The Niners, unfortunately, were unable to take true advantage of this, rushing for a combined 66 yards and averaging 2.9 yards per carry in the process. A big reason, arguably, was losing running back Matt Breida to an ankle injury early after he managed only six yards on five carries. Shanahan expects Breida to be ready to go after missing last week, however, and the second-year pro is still averaging 5.6 yards per attempt -- tied for second best in the NFL behind Lindsay.

Ahkello Witherspoon on the Ascent Again?

The first half of 2018 wasn't kind to second-year conerback Ahkello Witherspoon who, after an impressive rookie campaign, reverted to being a liability and seemed always prone to giving up at least one big play per game.

Over the past few weeks, however, much of that has changed. The Niners Wire's Kyle Madson explained:

There's been a turnaround through the last few weeks that points to more of what we saw from the 23-year-old in his rookie season. Witherspoon has allowed eight catches for 97 yards and no touchdowns on 23 targets since Week 10 according to PFF. Quarterbacks have earned a paltry 48.6 quarterback rating when throwing his way. A stark contrast to the 98.0 rating he's allowed this season.

Granted, Witherspoon didn't have to worry much about a banged-up Broncos wide receiver corps last week. But with Seahawks wideout Doug Baldwin (hip) questionable for Week 15, the same scenario might repeat itself.

Sunday's matchup should be a good indication where the arrow is pointing for Witherspoon.

Nick Mullens' Chemistry with Dante Pettis

While most things didn't go well for the 49ers in Seattle, at least there was a nice little rapport between quarterback Nick Mullens and wide receiver Dante Pettis. Mullens ended up passing for 414 yards during the game, which is a far greater measure of success over many a Niners quarterback playing at CenturyLink Field the past few years.

Pettis recorded 129 of those yards on five receptions plus two touchdowns. And that contest wasn't just a proverbial "flash in the pan" either.

Over the past three weeks, Pettis has averaged 85 receiving yards per game and has four touchdowns during that same span. After a slow start to his rookie year, the second-round NFL Draft pick has seemingly found his stride and should be a key offensive focal point for San Francisco during the game.

Keeping Bobby Wagner from Making an Impact

Seahawks linebacker Bobby Wagner literally took over Week 13 from a defensive standpoint. If you're unsure how, just consider this:

Wagner forced and recovered the fumble by 49ers running back Jeff Wilson. Questionable as it was, it still counted. So did Wagner's pick-six interception off Mullens, which ensured any San Francisco comeback would fall well short. Tackles galore, a sack, multiple passes defended and all-around disruptive play made Wagner the force against which the Niners had to contend two weeks ago.

And it didn't go well.

Wagner is the kind of player Shanahan will have to scheme against during this contest, looking to remove him from plays by the combination of misdirections, pick plays whatever means to get the ball moving away from the linebacker's direction. Easy? No. Necessary for a 49ers upset? Absolutely.

However that goes, the 49ers and Seahawks will kick off on Sunday, Dec. 16 at 4:05 p.m. ET from Levi's Stadium in Santa Clara, California.