What are the Lions' top needs on defense?

After taking a look at the Detroit Lions' depth chart on offense, it's now time to examine their depth chart on defense. As a reminder, this depth chart is based on the current roster, and it includes soon-to-be free agents and players who finished the season on injured reserve. It's meant to be an overview of where everything currently stands, and it's meant to show what the Lions' biggest needs are going forward. Take a look:

(Note: Players highlighted in yellow are set to become free agents in March.)

If you just count the players who spent 2014 on the 53-man roster, more than half of the Lions' defensive linemen from last year are headed for free agency. That includes three of the Lions' top four defensive tackles. That's by far the biggest story for the D-line and really the defense in general. If you take the free agents out of the equation, the Lions would be starting Caraun Reid and Xavier Proctor at defensive tackle right now.

Of course, it needs to be said that the Lions probably won't have too tough of a time re-signing Andre Fluellen for the eighth or ninth time, and I would think that re-signing C.J. Mosley is something they could pull off at a pretty affordable rate. Re-signing Ndamukong Suh and Nick Fairley is obviously a much different story. Suh could very well become the highest-paid defensive player in NFL history, so the Lions are going to have to open up their checkbook to re-sign him. If he is in fact re-signed, that would make bringing back Fairley a bit more difficult, but at least one of these players needs to be with the Lions in 2015, and Suh is the obvious pick if they can only have one.

At defensive end, the situation is much more encouraging with both starters still under contract. Both backups are set to become free agents, but I can't imagine Darryl Tapp or George Johnson will be out of the Lions' price range if the team wants them back. And even if neither player returns, the Lions have Larry Webster and Devin Taylor ready to step in as the backups.

The situation at linebacker is also pretty encouraging. Assuming Stephen Tulloch makes a full recovery after tearing his ACL, and assuming he isn't released as a cap casualty, the Lions should be able to shift Tahir Whitehead back to the strongside spot. Whitehead really performed well as Tulloch's replacement inside, but being able to shift him back outside would really be nice for depth reasons, especially if restricted free agent Josh Bynes is re-signed. That would give the Lions a bit of an overflow of strongside linebackers, but chances are all of these guys will be shifted around to other positions on a fairly regular basis in order to ensure that there is depth at all three spots.

Rashean Mathis has already said that he wants to return to the Lions, meaning both starters at the outside cornerback spots should be back. The Lions will have to start thinking about a future replacement for Mathis, but for 2015, they should be set as long as Mathis is re-signed.

The Lions should also be set at safety in 2015 with both Glover Quin and James Ihedigbo under contract. Re-signing Isa Abdul-Quddus would be nice given that Ihedigbo had some injury issues, but other than that, there's not really anything up in the air at safety.

One spot that could be up in the air is nickelback. The Lions lost both Bill Bentley and Nevin Lawson to season-ending injuries early in 2014, leading to various players stepping in at the nickel cornerback spot. Cassius Vaughn and Don Carey got the bulk of the work there down the stretch, but that was a shaky spot for the Lions defense. If Bentley and Lawson both make full recoveries, the Lions could decide to simply roll with them, but if there's any uncertainty about their status, it would be wise to make an upgrade.

Finally, as a bonus, here's a look at where things stand with the Lions' specialists. Chances are Don Muhlbach will be re-signed as long as he wants to keep playing, and Matt Prater has already made it known that he wants to stay in Detroit. It remains to be seen what kind of contract he will be after, but the Lions would be wise to bring back Prater considering what a disaster their kicking game was last season before he arrived.

Recap

Everything really revolves around the defensive tackle position. If the Lions are able to re-sign Suh, they will at the very least be able to let out a sigh of relief. And if they are able to re-sign Suh and Mosley, that position will be in very good shape no matter what else happens. If they only bring back Fairley or there's an even worse scenario where everybody departs, though, defensive tackle will pretty clearly be the biggest need this offseason.

Beyond that, the rest of the defense is in pretty good shape. The most notable free agent in the back seven, for example, is Mathis, and he's interested in coming back and will probably be signed to a relatively affordable deal. There are a few spots where depth could be an issue depending on who else is re-signed, and either way, the Lions certainly need to consider upgrading a spot or two in the secondary. Generally speaking, though, the Lions are in fine shape at just about every position but defensive tackle. What happens there will have a large effect on the rest of the defense and the team in general, but that's really the only position of great concern at this point.