Before the season, neither the Detroit Lions nor the Miami Dolphins were predicted to do that much. Yet eight games into the season, they rank as two of the league’s biggest surprises.

Detroit entered the season with a new head coach, Jim Caldwell, and the Lions are 6-2 and lead the NFC North. Miami had three straight seasons of being .500 or worse and was entering a critical year for quarterback Ryan Tannehill’s development. After three straight wins, the Dolphins are 5-3 and in the midst of the AFC playoff race.

So what happens Sunday? NFL Nation Dolphins reporter James Walker and Lions reporter Michael Rothstein break down what might happen at Ford Field.

Rothstein: Since he completed less than 50 percent of his passes in Week 3 against Kansas City, Ryan Tannehill has looked like a different quarterback. He is completing 68.8 percent of his throws and has 10 touchdowns to four interceptions, and the Dolphins have won four of five games. Has something drastic changed in his game?

Walker: Playing well isn't foreign to Tannehill. But playing well over a long stretch was the issue. For the first time in three seasons, we are finally seeing a good level of consistency from Tannehill. He's had three triple-digit passer ratings in the past five games. Tannehill deserves a lot of credit for improving his play speed and decision making. But credit also goes to the Dolphins' first-year offensive coordinator, Bill Lazor. He's done a good job of eliminating what Tannehill doesn't do well -- for example, throwing the deep ball -- and highlighting strengths such as short and intermediate passing and his mobility. It's a good combination of the coaching and quarterback improving simultaneously.

Lions All-Pro receiver Calvin Johnson is expected to return Sunday from his ankle injury. Michael, do you think the timing is right, and what kind of impact will he have?

Rothstein: It's about time he returned, frankly, because the Detroit offense needs him. The first time he sprained the right ankle, the Lions let him push it, but when he aggravated it, they made it clear they would let him take however long he needed to heal for both short-term success and long-term health. That was a month ago. He looked crisp in practice and seems to be as close to 100 percent this far into a season as he has been in a long time. The impact should be massive. With Johnson out, QB Matthew Stafford and WR Golden Tate found a strong connection. Now teams will have to account for Tate and Johnson, along with the potential of the Lions' running backs. That's a lot to deal with for any defense.

Since we're talking about Johnson, Miami has CB Cortland Finnegan, who has experience covering Johnson at multiple levels. Will Finnegan match up with the receiver, or will the Dolphins try a different type of scheme? This is Miami defensive coordinator Kevin Coyle's first time to scheme against Johnson, though when Coyle was the defensive backs coach in Cincinnati, he did face the receiver.

Walker: The Dolphins usually mix it up between Finnegan and cornerback Brent Grimes. But if the Dolphins put one player primarily on Johnson, it will probably be Grimes. He is a little more athletic and quicker out of his breaks. Grimes also is hot. He picked off Chargers quarterback Philip Rivers twice last week while covering receiver Keenan Allen. Miami's locker room has had high praise for Johnson this week. Finnegan called him a Hall of Famer and Coyle said the defense will have its hands full. But Miami has a quiet confidence that its No. 2-ranked pass defense will perform well.

Many people in Miami know Lions RB Reggie Bush, who has missed time with an ankle injury. Could he return and impact this game against his former team?

Rothstein: I expect Bush to play, but his impact won't be as great as Johnson's. The Lions have struggled rushing most of the season (31st in the NFL), and a lot of that has been with Bush. While he will have a role, he will likely split carries with Joique Bell and Theo Riddick, who is Bush-like and made an impact in Bush's absence. Detroit knows it needs to get more out of those guys.

So James, one of Detroit's other issues has been protecting QB Matthew Stafford. This seems to be a pretty strong matchup for Miami DE Cameron Wake. What makes him unique?

Walker: I always appreciated Wake's story because nothing was ever given to him. He was undrafted and had to go through the CFL before getting his chance in the NFL. He's never let go of that chip on his shoulder, despite multiple Pro Bowls. Wake still plays every year as if he has something to prove. But the difference this year is that Wake has a lot of help. Olivier Vernon has developed into a solid defensive end in his own right, and Miami has a plethora of good defensive tackles (Jared Odrick, Randy Starks, Earl Mitchell) to rotate during games. This group has worn out a lot of opposing offensive lines this year and will look to do the same against Detroit.

Finally, the Lions' defensive line is equally as good. How does it match up with Miami's offensive line in this game?

Rothstein: Considering Miami is right in the middle of the NFL at allowing sacks (on 5.9 percent of the Dolphins’ dropbacks), it could be a tough day for Tannehill. The Lions have faced quarterbacks with at least some mobility this season -- a still-recovering Cam Newton, Teddy Bridgewater and Geno Smith -- and have done a good job keeping them pretty hemmed in the pocket. The wrinkle with this week’s defense, though, is it will be without defensive tackle Nick Fairley, who is out with a knee injury. Not having Fairley on the defensive line could mean more double-teams for Ndamukong Suh and Ezekiel Ansah -- and therefore that fraction of more time for Tannehill to make decisions and avoid sacks. But Detroit will still get pressure. Of that there is little doubt.