In four weeks of football, we’ve seen some surprises. The Kansas City Chiefs look like the best team in football heading into NFL Week 5, while the New England Patriots are .500. The Buffalo Bills sit atop the AFC East, and the Los Angeles Rams lead the NFC West.

The early part of the season tends to produce such anomalies. Chances are, we’ll be laughing about most of them come Thanksgiving. But not all will be short-term trends. This week, some will try to keep their hot starts intact. Others will try to turn it around.

Here is each team’s player with the most to prove in Week 5.

Los Angeles Chargers: Joey Bosa, defensive end 

After lighting the league on fire in his rookie season, Bosa was tabbed as a potential Defensive Player of the Year dark horse heading into the season. Instead, he’s been pedestrian at best. According to Football Outsiders, Bosa has just 3.5 pressures in four games, though 2.5 are sacks. He also has a middling 66.8 PFF grade. With the Chargers facing a terrible New York Giants offensive line, this is the week where Bosa has to look like himself again.

New York Giants: Eli Apple, cornerback

Apple has been the weakest link in the defense of Big Blue thus far. In addition to a couple high-profile errors, he has a terrible 38 percent success rate and is allowing 7.9 yards per pass, per Football Outsiders. Apple’s play has led to him being a consistent target in an otherwise solid Giants secondary. If New York is going to recover from their 0-4 start, Apple needs to put this sophomore slump behind him.

Buffalo Bills: Zay Jones, wide receiver

Jones has gotten off on the wrong foot to start his NFL career. Expected to be a target magnet for Tyrod Taylor before the season, the rookie has just four receptions in as many games. And it’s not for a lack of targets; Taylor has looked his way 17 times. That adds up to a 23.5 percent catch rate. Avert your eyes. This has to change, and fast.

Cincinnati Bengals: Brandon LaFell, wide receiver

The Bengals’ passing offense has struggled in part because A.J. Green is the only dependable target Andy Dalton has at the wide receiver position. Though Dalton has subsisted by targeting tight ends and running backs, that model is not sustainable – at least not without one other wideout to draw attention. LaFell is supposed to be that player. However, with just 76 yards in four games, he’s been a mere sidepiece.

New York Jets: Matt Forte, running back 

Forte’s grip on the starting job fell apart last week against the Jacksonville Jaguars. Given the chance to take the reins with Forte out, Bilal Powell went for 163 yards and a brillian touchdown. Even Elijah McGuire – normally the third-stringer – had 93 yards on 10 carries. Though Forte is still dealing with an injury and could miss Sunday’s game, he needs to play and play well, or else Powell will put an end to the timeshare. 

Cleveland Browns: Jamar Taylor, cornerback

Taylor was one of football’s pleasant surprises last season, quietly putting together a great year in Cleveland. However, the hardest part of breakout seasons is usually following up on them. So far, Taylor has failed entirely in doing so. Through four games, he has an atrocious 36 percent success rate, per Football Outsiders. His PFF grade – a solid 82.0 last year – has plummeted to 39.6 in 2017. Cleveland’s secondary should be one of its few strengths. Taylor has to make it happen. 

Carolina Panthers: Matt Kalil, left tackle

When Kalil signed a five-year, $55 million deal with Carolina during the offseason, it was widely panned, in large part because Kalil has long been one of the worst tackles in football. For lack of a better description, Kalil has been himself to open this season. To put it bluntly, that is not worth the $11 million average salary he’s being paid, or even 10 percent of $11 million. Kalil must prove to everyone that GM Dave Gettleman – who has since been fired – wasn’t off his rocker when he offered that contract. He’s officially questionable to play (groin) Sunday against a Detroit defense that has been much better than expected this year.

Detroit Lions: The defense

Detroit’s defense has gone from 32nd in the league last season in efficiency, as measured by DVOA, to fifth through four games of this season. Forgive us for being skeptical. The Lions didn’t splurge for pass rushers in free agency. Outside of the early rounds of the draft, they did little to address the defense. This is largely the same personnel as last year, with the exception of rookie linebacker Jarrad Davis and a few more rotational pieces. Four weeks is rarely indicative. The Lions must prove they aren’t pretenders.

San Francisco 49ers: DeForest Buckner, defensive lineman

DeForest Buckner

After four games, it looks like this could be the year where Buckner pops. He has 10 pressures, per Football Outsiders, a sack, and leads all interior defenders in PFF grading. Buckner flashed potential in his rookie year, but this is a whole new level. If he keeps playing like this, Buckner will be an All-Pro. Let’s see him prove he can do just that.

Indianapolis Colts: Jack Mewhort, right guard

Before the year started, it looked like Mewhort would be one of the only reliable pieces of Indy’s offensive line. Instead, he’s been one of the worst. Mewhort has a terrible 46.8 PFF grade. The Colts have struggled badly to run the ball up the middle, in large part because of his struggles. We expected this kind of play from most of the line, but not him.

Tennessee Titans: Adoree’ Jackson, cornerback

The Titans’ entire secondary has struggled, and nobody has struggled more than Jackson. A first-round pick this year, Jackson has just a 44 percent success rate, per Football Outsiders. He also ranks 90th among corners in PFF grading with a 43.7 mark. There’s always some sort of learning curve, but it shouldn’t be this steep for Jackson.

Miami Dolphins: Jay Cutler, quarterback

After an embarrassing 20-0 loss to New Orleans in which Cutler was outwardly apathetic at times, we’re left with one question: Why did Jay Cutler come out of retirement? Not only is he playing badly, but Cutler just doesn’t look like he cares. Why should he be here instead of at home with his feet up if this is what it’s going to look like? Right now, it’s tough to argue the Dolphins are better off for his presence. At this point, Cutler has to prove he should be playing football.

Arizona Cardinals: Tyrann Mathieu, cornerback

The Honey Badger is going through a rough stretch. In the early part of the year, Mathieu is giving up 1.83 yards per route covered, per Pro Football Focus. His PFF grade is an abysmal 37.9. More than likely, this is just an extended slump. However, given the state of Arizona’s secondary without Mathieu at his peak, it’s hard not to be worried. The Cardinals won’t escape Philadelphia with a win this weekend unless Mathieu starts ramping it up.

Philadelphia Eagles: Rasul Douglas, cornerback

Rookie cornerbacks struggling is not a new phenomenon. However, Douglas is – as of now – a starting player and a massive liability. Not only is he giving up 8.2 yards per pass, but 4.6 of them are coming after the ball is caught, per Football Outsiders. When it comes to yardage after the catch, all of Philly’s cornerbacks have struggled. However, the others have made up for it with strong coverage. Except Douglas. That cannot continue.

Jacksonville Jaguars: Blake Bortles, quarterback

The Jaguars have the personnel to be in the playoffs. The defense is a top-10, maybe even top-5 unit. Rookie running back Leonard Fournette has as much talent as anyone at the position. Even without Allen Robinson, the receiving corps is solid, the offensive line is passable. Yet, the Jaguars are 2-2, which includes a loss to the New York Jets. And you don’t have to look very far to figure out why. Bortles has not been atrocious as he’s been in the past, but this isn’t good enough. He’s killing them softly. With the schedule getting tougher over the next two weeks, his struggles will be on display unless there’s some improvement.

Pittsburgh Steelers: Ramon Foster, left guard

Foster has been one of the league’s better guards for a long time. By PFF grading, he had the best year of his career in 2016, despite hitting 30. At 31, the aging curve seems to be taking effect. Foster has a 59.6 PFF grade through four games this season. For a team like the Steelers, whose offensive line quietly propels the run game, that’s a huge problem. Much criticism has been directed at Le’Veon Bell, however, the offensive line carries some fault in the run game’s slow start. That includes Foster.

Baltimore Ravens: Mike Wallace, wide receiver

Wallace finally got the engine running in Baltimore’s loss to Pittsburgh last week, going for six receptions and 55 yards. Though those totals are modest, they both eclipsed anything Wallace had done in the prior three games. At 31 years old, it’s tempting to declare Wallace finished, but Week 5 is too early to go around making such declarations. This Sunday against Oakland will, however, be a good test case. Wallace is meant to be the top receiver in this offense, let’s see him play like it.

Oakland Raiders: Marshawn Lynch, running back

Since his delightful Week 1 performance, Lynch has struggled. He’s averaged just 2.78 yards per carry for a total of 75 yards – one less than the 76 he ran for on Opening Day. Sitting out for an entire season before coming back – at age 31, no less – seems to be taking its toll. Things won’t get easier for Lynch as the wear-and-tear kicks in. However, it’s still early. There’s time to turn it around. But that has to start soon.

Seattle Seahawks: Tyler Lockett, wide receiver

The Seahawks are missing a dynamic playmaking receiver on offense, in large part because Lockett is not fulfilling his role as a dynamic playmaking receiver. Lest we forget that before he went down at the end of last season, Lockett was a big play machine.  Though he’s averaged 13 yards per reception this year, Lockett has yet to leave his imprint on a game in a meaningful way. For the Seahawks to start looking like title contenders again, Lockett needs to be an impact player.

Los Angeles Rams: Robert Quinn, outside linebacker

There are few bones worth picking when it comes to the Rams. However, It is a bit disheartening to see Quinn with just three pressures in four games, per Football Outsiders. The former All-Pro is finally healthy. However, just doesn’t seem to be the same player as before. He has a terrible 44.3 PFF grade thus far. Of course, there’s still time for Quinn to prove this all wrong.

Green Bay Packers: Damarious Randall, cornerback 

There’s a case to be made that Randall has been the worst cornerback in football during the season’s first quarter. He’s given up 10.5 yards per pass on a 33 percent success rate, per Football Outsiders. Randall is also one of just five corners who play regularly to give up over two yards per route covered, according to PFF. Forget about the Packers, at this rate, Randall will soon be playing for his job.

 Dallas Cowboys: Jaylon Smith, linebacker 

Dallas Cowboys linebacker Jaylon Smith

The fact that Smith is even playing professional football after a gruesome knee injury seemed to end his career in the Fiesta Bowl two years ago is a miracle of modern medicine. Playing professional football well, however, is a different story. Smith’s mobility has clearly been an issue and it was on full display last week with fellow linebacker Sean Lee missing. He has just a 40.2 PFF grade as well. With Lee potentially out this week as well, that won’t fly.

Kansas City Chiefs: Mitchell Schwartz, right tackle

The Chiefs’ offensive line has been its biggest problem in the early part of the year. Given the injuries to its interior, that’s not especially surprising. Schwartz’s performance, however, is another story. Since coming into the league, he’s consistently been one of the best right tackles in football. However, he’s started this year on the wrong foot – a 53.4 PFF grade through four games. That’s played no small part in Kansas City’s 32.6 percent pressure rate, per Football Outsiders. It may just be an early season slump, but Schwartz has to snap out of it.

Houston Texans: Bernardrick McKinney, linebacker

McKinney is one of few players on Houston’s defense to struggle early this season. Outside of two sacks in Week 2 against the Bengals, the third-year linebacker has largely failed to make much of an impact. He has a dismal 43.8 PFF grade — a huge drop from his 79.9 mark last season. If McKinney can return to form, Houston’s front seven goes from good to great.

Minnesota Vikings: Latavius Murray, running back 

Murray was largely relegated to the sideline for the first four games as rookie running back Dalvin Cook became the Vikings’ workhorse. But after Cook tore his ACL last Sunday, the job is Murray’s to lose. Murray has to remind Minnesota why it signed him in free agency. He’s had just 14 carries to date – seven of them last Sunday – and has gone for an average of 2.7 yards per carry. Unless that gets better, the Vikings’ offense may fall apart without Cook.

Chicago Bears: Mitchell Trubisky, quarterback

It took all of four weeks for head coach John Fox to succumb to the pressure and make Trubisky the starting quarterback.  Proving that he belongs on the football field is a huge burden even without the added background. The Bears didn’t just take Trubisky second overall, they traded up to do it and were universally panned. Trubisky started for just a year in college. Now, he’s being thrown to the sharks. Let’s hope he learns to swim.