Fantasy football research never stops, and roles change drastically from one week to the next. That's where our fantasy football mailbag comes into play.

Have a question about a certain player, team, strategy, or anything football? Shoot us a question on Twitter or send an email to Jim.Sannes@FanDuel.com, and we can talk anything fantasy football related -- even daily fantasy football.

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Now, let's answer some questions.

Email submission from Dana Fisher:

In one league I've been QB Streaming all year. Now most are picked up and I'm stuck with Flacco this week. Should I pick up one of these lesser options: Barkley, Kap, Fitzpatrick(if he plays) or RGIII even? I'm a big underdog going against Brady and Julio.

Joe Flacco really isn't a bad option this week going up against the Pittsburgh Steelers. He has multiple passing touchdowns in four of the past six games, and the Steelers rank 21st against the pass this year, according to numberFire's schedule-adjusted metrics. However, with an implied team total of 19.75 for Flacco's Baltimore Ravens, it may not be bad to give Matt Barkley a look.

Barkley's implied team total is much more friendly this week at 22 with the over/under inflating to 47 points after opening at 45. The Chicago Bears are three-point underdogs, which is a bit scary, but Barkley's matchup and efficiency have him in a respectable spot.

Washington ranks 25th against the pass this year, and they have allowed five of the past six passers they have faced to top 300 yards. Barkley ranks 15th in Passing Net Expected Points per drop back, numberFire's metric to track the efficiency of quarterbacks, meaning he should be able to move the ball against this team. You may not feel super comfortable plugging in a player with 212 career pass attempts, but Barkley's situation this week does appear a bit safer than Flacco's.

Email submission from Jonathan Buster:

I have L Murray locked in as my RB1 this week, but I have both Bilal Powell and Ty Montgomery too. Of those 2, who is the better flex play? Thanks

You've got two great options here in Bilal Powell and Ty Montgomery, so at least feel encouraged by that. Powell has at least 160 yards from scrimmage in back-to-back games, and Montgomery is coming off of a game in which he racked up 162 yards and 2 touchdowns on the ground. You really can't go wrong. But because of a situation more conducive to touchdowns, Montgomery holds the edge.

Montgomery checks every box we look for in a running back. The Green Bay Packers are at home, they're favored by 6.5, and they're facing a rush defense that -- as numberFire's Brandon Gdula mentioned in this week's Heat Check Fantasy Podcast -- has been on the decline recently. After playing 84% of the snaps last week, Montgomery has the floor and upside we want.

Powell does have at least one aspect of the equation in a hefty floor, meaning he's viable when the other options are less enticing. He had 12 targets in Week 15, and the New York Jets are in a situation where they'll likely need to throw a ton as 16.5-point underdogs against the New England Patriots. His involvement in the passing game means he's going to get volume this week, enough to make him a solid fantasy asset, but the lack of touchdown upside is what gives Montgomery the nod.

Email submission from Jonathan Martin:

Thank you once again for all of numberFire's hard work and dedication. Without you, I'd not be in our league's final. Your site has been my go to from pre-draft till now. Let's get to it. 1 pt PPR. Start 1 2 RB's: D. Johnson, L Miller, J Ajayi & R Kelley. Whatcha think to put me over the top? Thank you again and Merry Christmas!

David Johnson is the illest mamma jamma in all the land, so you're locking and loading that puppy no matter what the matchup is. As for the second spot, even though he's on the road, Rob Kelley is super interesting this week.

As mentioned above, the over/under for Washington's game against Chicago is on the rise, and it has pushed Washington's implied team total to 25 points. That's great news for Kelley, who has multiple red-zone carries in every game since he took over as the starter.

Additionally, the matchup here is ripe. Chicago ranks 28th against the rush on the season, though they will get linebacker Jerrell Freeman back from a PED suspension this week. Running backs had found success against the Bears prior to Freeman's suspension, and with fellow linebacker Danny Trevathan on injured reserve, this is a team we can target with opposing ground games. Kelley's risky in the event that Washington falls behind, but his upside here may make him the better play.

Want to have your questions answered in our mailbag? Submit your questions by tweeting @numberFire or sending an email to Jim.Sannes@FanDuel.com.