Linebackers
Jadeveon Clowney (HOU): He's actually a free agent in one of my 12-teamers, so I have to assume he's out there in some formats. As we all know, his value got squashed with the linebacker designation, but if dude is going to put up 26 points every so often, he's worthy of an add regardless. Heck, if he ever gets flipped back to a defensive line designation his value will skyrocket. In the meantime, grab and stash based on talent alone.
John Simon (IND): Don't normally endorse strong-siders, especially in 3-4 schemes but Simon has been serviceable the first three weeks of the season. He has a sack in each of the past two contests and hasn't dipped below 4 solos in any week. In larger leagues perhaps you add and hope he is a decent bye week plug-in.
Keenan Robinson (NYG): Let's not forget this guy had almost 100 combined tackles in 2014 and had decent numbers last season as well. He lost his starting job but can apparently produce nice fantasy numbers if called upon. Obviously not a weekly starter as his play will be generally dependent on the health of guys like B.J. Goodson (who the Giants love), but honestly, is he any better than Jonathan Casillas? Worthy of watching, especially if Goodson continues to spend time on the trainer's table.
Chandler Jones (ARI): He's available in a site experts' league (where Footballguys is 3-0, by the way) and like Clowney, could see a major jump in value if he's re-designated. Three straight weeks with 10 or more points and a 25-point outburst in Week 2 means you need to put him on your watch list, especially in larger formats.
Others to Watch: Chase Allen (MIA), Anthony Chickillo (PIT)
Defensive Linemen
Malcom Brown (NEP): Not much to choose from lineman-wise this week. We'll call your attention, though, to Brown, who has 9 solos (all in Weeks 1 and 3) from the tackle spot. Looks like he will get most of his production against run-centric teams, so if you are hurting at defensive line and especially if your league breaks out tackles from linemen, Brown's worthy of a look.
Mario Addison (CAR): For those in big-play leagues Addison is worth a look. The Panther defense desperately needs a pass-rusher, and at this point, it looks like Addison is the best they got. He won't pile up tackles but the occasional sack is certainly plausible. He had 9.5 last year and is well on his way to eclipsing that mark this season.
Other to Watch: Javon Hargrave (DT - PIT)
Defensive Backs
Terrance Mitchell (CB - KCC): Mitchell is benefiting from the "opposite shutdown corner" rule. Marcus Peters still does put up stats, but for the most part opposing quarterbacks look to the other side of the field. This means Mitchell should continue to put up solid stats. In cornerback-start leagues, he's a must-add right now.
Andrew Sendejo (S - MIN): One of the safer defensive back adds of the week. You know what you're going to get here. He's actually as consistent if not more so than his safety counterpart Harrison Smith, who consistently ranks as one of the top fantasy safeties in the game. Smith will get you huge games but Sendejo is a steady presence you can count on. Perfect bye week filler or DB2 in larger leagues.
Darian Stewart (S - DEN): Everyone is singing the praises of Justin Simmons and rightly so, but with the departure of T.J. Ward, Stewart has stepped his game up a bit. He won't put up flashy numbers but could provide consistent tackle stats. In larger leagues, keep an eye on Stewart because the Denver "D" can produce some numbers.