EAST RUTHERFORD, N.J. — They’ve had nine days of testing each other, five with pads on, and if it weren’t for Dan Campbell’s friendship with Brian Daboll, the Detroit Lions would be back in Allen Park this week mashing the same old faces.

Not that the Lions haven’t benefited from the first two weeks of training camp. The roster is more talented than it has been in years and the uptick in quality has offered good tests all over the field.

“You can feel the depth,” tight end Brock Wright said recently.

He is part of a group offensive coordinator Ben Johnson said is as deep, gifted and versatile as he has seen in his 13 years of coaching. And the room isn’t the only one packed with talent.

Where this leads is hard to say. Injuries can derail a season. So, too, can let-up, something Campbell has been guarding against since minicamp. The Lions head coach talked about his own experience as a player coming off a deep playoff run, only to have the next season fall apart.

“We’re always going to have to guard against — I’ll bring it up again, the complacency, the entitlement, the reputation. Like, ‘What is that? That’s nothing. We’ve got to go back to work,’” he said.

This was the first day of training camp, almost two weeks ago. And by all accounts — especially Campbell’s — the team has gotten good work in competing against one another.

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Still, no matter how much anyone enjoys battling their brother, it’s loads more fun to team up with your brother and battle the fella the next street over ... or the fellas in East Rutherford.

The Lions begin the first of two joint practices Monday against the New York Giants. It will be the second year in a row the teams have tussled during training camp. Last year, Daboll took his team to Allen Park. This year, Campbell is returning the favor.

Though for Campbell, the favor is all Daboll’s. Not every NFL coach believes in joint practices. Or finds them necessary. The Lions tried to convince Kansas City to do the same when they travel to Missouri for a preseason game later this month. Coach Andy Reid said no thanks.

It's understandable from Reid’s perspective: The Chiefs have won three Super Bowls in the past five years. They also have Patrick Mahomes. (These things are related.)

So, yeah, maybe Reid doesn’t think the extra juice a team can get from a joint practice is worth the risk of the increased intensity. Or maybe he doesn’t want to change what is working.

Which is why Campbell is grateful to Daboll, or to any coach willing to mix it up, as we head into the hazy — and hot — days of late summer. As Wright said last week:

“(There’s) always big excitement in a week like this. It's great going against our guys (and) getting the competition (at home). It’s also nice to get (a different look)."

The Giants offer that, and if quarterback Daniel Jones can rediscover the form he began to show late in the year two seasons ago, he’ll give the Lions' remade secondary a solid test. Jones tore his ACL last season and only played in five games. The Giants finished 6-11 a year after making the playoffs as a wild card and upsetting the Vikings in Minnesota.

New York is far from a Super Bowl contender, but has a promising defensive line and a handful of talented offensive players, including rookie receiver Malik Nabers, the No. 6 overall pick in April. He has created some buzz in East Rutherford the first couple weeks of camp.

He will be a good test for Carlton Davis III and the Lions’ own first-round pick, cornerback Terrion Arnold. It’s also a good test for the Lions' revamped defensive front to see if they can consistently pressure Jones.

Campbell began talking with Daboll in the spring about what they hoped to accomplish. They shared practice scripts with each other last week. The coordinators have all talked, too.

“We’re ready to go,” said Campbell.

"It’s just a matter of us getting out there. But it’s going to be good. We’re going to get unbelievable work out there. I’ve got a lot of trust in Daboll. He’s somebody that I have a lot of respect for and he’s a friend of mine and I just know that they’re going to do things right and so are we. So, we’re going to get really, really good work. Excited about it.”

Daboll laid out his expectations for the joint practice last summer when he arrived in Detroit. It’s a safe bet they haven’t changed.

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It’s about practicing the right way “against a really good team,” he said. “Will be a good test for us.”

There are some ground rules both coaches laid out a year ago, and those haven’t changed, either.

“You have a bunch of competitive people that are hitting each other,” said Daboll. “We’re going to try to take care of one another, keep people off the ground, stay away from the quarterback, just practice the right way like you’re practicing against your team. But again, the competitive juices flow.”

Encouraging those juices while making sure no one gets hurt is the balance here. As Wright noted, the players naturally up the intensity when battling an outside opponent. That helps the coaches evaluate, and the players self-scout.

The two joint practices will lead to each team’s first preseason game Thursday night at MetLife Stadium, near the Giants’ practice facility. The game will also be a good tool as the staffs begin to think about whittling down the roster and figuring out tentative depth charts.

This week will be a good chance for Daurice Fountain, for example, to keep building his case for the No. 3 receiver. It will also be Hendon Hooker’s first chance as a Lion to go live in the quarterback spot.

The practices and game will bring a bit more clarity to a couple other spots with stiff competition, too, such as safety, nickel back and linebacker, where the coaches have spent two weeks rotating several players to see what they’ve got — or how they’ve improved.

Joint practices may not be necessary for every team, clearly. But for Campbell and his Lions, they are critical for development and for learning how to handle physicality. Because even though the joint practices are not regulated like NFL games, the intensity is a step up from regular practice.

No wonder Campbell was smiling Friday.

Contact Shawn Windsor: swindsor@freepress.com. Follow him @shawnwindsor.

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This article originally appeared on Detroit Free Press: Lions ready to hit someone else — respectfully — in practice at Giants