Linebackers
Ray-Ray Armstrong (SFO): Goes without saying but with NaVorro Bowman now up the freeway in Oakland, Armstrong is a must-add in all formats. He was already putting up solid fantasy numbers since the rookie Reuben Foster's been sidelined but he should be the leader of the Niner linebackers at this point. If he's still available in your league, jump now before it's too late.
Elijah Lee and Brock Coyle (SFO): If Ray-Ray is gone-gone, take a flier on one of these guys. A couple depth chart sources list Armstrong still lining up on the weak side (and may if Foster remains out) with Coyle manning the middle. The real guy to watch is Lee, who came out of Kansas State a little on the underrated side. Lee was drafted by the Vikings but has since made his way west to the Niners and could be a name to watch if he gets some snaps.
Connor Barwin (LAR): For those in "big play" formats, Barwin is worth monitoring. He is a perfect fit for Bum Phillips' defense (he excelled in it before) and while it'll be tough to replicate the 14.5 sacks he accrued in 2014 under Philliips, he may be a cheap source of sacks and the occasional 3+ solo outing.
Matt Judon (BAL): Whoa, where'd that come from? 30-plus points is no joke in any format. He absolutely crushed the Bears and the spot he's currently lining up at has in the past been quite fruitful for fantasy owners. Maybe you wait a week to see if he can duplicate the stats or perhaps you invest now. Only 25, he could be a very valuable piece eventually.
Mychal Kendricks (PHI): Kendricks happens to be available in a Footballguys experts leagues and I'm not sure why. Aside from a ho-hum 2016, Kendricks has been more than servicable; at worst a decent LB3 or bye week plug-and-play. We like the remaining schedule from a tackle opportunity standpoint so if you need a cheap LB3 with decent upside, give the Eagle a spin.
Others to Watch: Kareem Martin (ARI) and Brennan Scarlett (HOU)
Defensive Linemen
A'Shawn Robinson (DT - DET): The pick-six was no fluke. Robinson has been filling up the box score with non-tackle plays and could be a solid add, especially in leagues that break apart tackles and ends. After the Lions' bye, Robinson has a very juicy schedule. The next six contests could result in solid fantasy production.
Michael Pierce (DT - BAL): Here's another young tackle that has been filling the box score up nicely. Along with non-tackle stats, Pierce has two contests with 5 or more solos. That is a good sign, especially for an interior lineman. This is a shallow position so you need to keep your eyes on guys like this.
Other to Watch: Morgan Fox (DE - LAR)
Defensive Backs
Tre Boston (S - LAC): The Bolts have been searching for a quality replacement to Eric Weddle for years now. Jahleel Addae is servicable but forgettable. Boston has been a key ingredient to the Chargers' defensive improvements of late and his fantasy production is showing the fruits of that labor. He'll never put up DB1 type stats but knowing what this spot typically produces makes him a fairly safe DB2.
Morris Claiborne (CB -NYJ): Claiborne is an ultra-talented football player. Make no mistake about it. Still only 27, he most definitely has a few good yeasr left in him. And if his 15 solos over the past two contests is any indication, he can still get it done. He'll get you a pass defense or two just about every contest as well. That makes him a solid DB2/bye week filler or perhaps even a weekly starter in leagues that carve safety and cornerback out.
Justin Simmons: (S - DEN): I'll add him here only because he happens to be available in one of my 12-team IDP dynasty leagues. He may be long gone in your league but you never know. Simmons is an athletic freak that the Broncos felt comfortable enough with to let longtime starter T.J. Ward walk. He's a ballhawk that can help in the run game. He's coming along a little slowly in the 2017 season but the tackles and big plays will most certainly come.
Others to Watch: Rashaan Melvin (CB - IND) and K'Waun Willams (CB - SFO)