The Washington Redskins started the 2019 season off 0-5. Things looked miserable and they decided to make a coaching change, firing head coach Jay Gruden.

In his place, Bill Callahan was promoted to interim head coach. They won their first game under him in Week 6 and moved to 1-5.

Yes, the game was against the winless Miami Dolphins and they barely won, but a win is a win.

In Week 7 they face a much tougher task, the 5-0 San Francisco 49ers. If the Redskins are to pull off the massive upset, they'll need some big things to happen. If they do win, here are four reasons it happened.

Running Game

The 49ers have one of the best rushing defenses in the NFL. They are sixth in the entire NFL with just 87.2 rushing yards allowed per game.

Meanwhile, the Redskins running game has been bad all year. That is, all year until last week.

Again, you could argue it was against the Dolphins. However, it could also have something to do with the new system in place.

One of the first things Callahan said when he took over in Washington was they wanted to focus on the run. That's right up Adrian Peterson's alley.

Despite the issues with the line, they're built for this as well. I can't stress enough how great Ereck Flowers has been at left guard. Brandon Scherff is a stud run block as well and Chase Roullier is solid. Expect a lot of runs up the middle.

They are going all in on this too. The Redskins have even signed a fullback (Michael Burton). That hasn't been a position of prominence for them since the days of Darrel Young.

Clearly, the plan is to run the ball with Peterson early and often. Yes, the 49ers have been great against the run. The difference here though is it doesn't look like the Redskins will abandon it.

With Peterson's strong style of run, it could lead to a few big plays. Those could be the difference.

Terry McLaurin

Speaking of how good San Francisco's defense is. Their pass defense is even better than their run defense. The 49ers are allowing just 150.2 passing yards per game. That's the best in the NFL.

Meanwhile, the Redskins passing offense isn't good.

Case Keenum has looked bad at quarterback after starting off the year with two really strong weeks. Even against the Dolphins he barely completed 50% of his passes (13-for-25) with just 166 passing yards.

He did manage to throw two touchdown passes though, and that was mainly because of his best weapon, Terry McLaurin.

McLaurin has been an absolute stud in his rookie year. Through five games, McLaurin has 23 receptions for 408 yards and five touchdowns.

Washington wasn't supposed to have any type of passing offense this year and he's changed that completely. McLaurin is constantly running mouth-watering routes. He makes tough grabs and uses his blazing speed to burn past the defense.

There's no reason to believe he can't find a way to break off a big play or two against the 49ers. That might be all it takes to keep a lead.

Defense

The Redskins defense hasn't looked great this year. However, they've definitely had their moments over the last few weeks.

Landon Collins looked fantastic in Week 5, they've had a few cornerbacks look solid (I'll get to that later) and the defensive line is legit.

Middle linebacker Jon Bostic looks like he's getting more comfortable as well. Ryan Kerrigan and Montez Sweat don't have big sack numbers but you can't expect them to be contained for too long.

That line is the star attraction though and that's important. The 49ers have a great rushing attack with a three-headed monster of Matt Breida, Tevin Coleman and Raheem Mostert. With those three, they can wear down an offense while keeping them fresh in a rotation.

Washington's defensive line can counter that pretty well though.  Da'Ron Payne is a freak at defensive tackle and Matt Ioannidis and Jonathan Allen are dual-threats on the outside. Meanwhile, Tim Settle is a superb backup and they won't skip a beat when he's in. That will keep them fresh as well.

Quinton Dunbar

Now on to that cornerback. A lot of people expected Quinton Dunbar to take a step forward in 2019. He hasn't taken a step, he's taken three or four.

Dunbar's been great all year and his last few weeks have been the icing on the cake. Dunbar had a two interception game against the New York Giants a few weeks ago and had another pick against the Dolphins.

Most importantly though, he's not all about the interceptions. Dunbar's been fantastic in coverage and is showing serious improvement in tackling. He made quiet a few nice plays over the last few weeks, including stuffing some screen attempts against Miami.

Even though he's still underrated by many (seriously, we didn't even have a picture of him on file to put here) Dunbar gives the Redskins a pretty legitimate number one cornerback (easily ahead of Josh Norman at the moment).

While he might not be Jalen Ramsey or Stephon Gilmore, Dunbar is pretty special. With Jimmy Garoppolo struggling at quarterback for San Francisco this year, Dunbar is the type of corner that can give him fits, especially with that great defensive line pressuring him.

The Redskins defense is starting to correct itself and Dunbar is a main reason why. He could be a main reason why they pull off the upset victory in Week 7 agains the 49ers.