Close to 70,000 fans will pile into Levi's Stadium on Sunday afternoon to watch the San Francisco 49ers open their 2017 season against the Carolina Panthers. It will be the first regular season game for Kyle Shanahan as a head coach and the first for an overhauled roster that has drawn low expectations from the national media.

Among those thousands of fans will be two sets of parents. Chris and Martha Thomas, parents of rookie 49ers defensive lineman Solomon Thomas, and Ed and Lisa McCaffrey, parents of rookie Panthers running back Christian McCaffrey. It will be a homecoming of sorts for Christian's father, Ed, a former wide receiver who also played at Stanford and played a season with the 49ers in 1994, during which he won a Super Bowl. He went on to win two more Super Bowls with the Denver Broncos, where Kyle Shanahan's father, Mike, was the head coach after being Ed's offensive coordinator in San Francisco.

The Thomases and McCaffreys will sit with each other as they observe their children's NFL debuts. The two families are linked together by a close friendship between Solomon and Christian.

Thomas and McCaffrey got to know each other at the U.S. Army All-American Bowl, which is a game that showcases top high school players. Their relationship continued to grow throughout college. They would put in extra work together and hang out with each other outside of football. They became roommates during their junior years at Stanford.

"We agreed to cheer for each other's kids," said Martha Thomas, according to the San Francisco Chronicle.

In April, following his selection by the 49ers in the draft, Thomas shared that he and his roommate took their competitiveness to a specific board game.

"We had ridiculous Connect Four tournaments in our dorm room last year," Thomas told KNBR. "Between watching film and movies, we had Connect Four. We'd have the scoresheet out that Christian [McCaffrey] made. We would just go at it. It got pretty intense. The board almost broke a couple of times."

Thomas admitted that McCaffrey was the better player when it comes to the board game but liked the idea of settling the score on the football field.

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"It'll be good (going against Thomas)," McCaffrey told Charlotte area reporters on Wednesday. "It'll be pretty familiar. We did it a lot the past three years. I'm excited, man. That's one of my best friends in the whole world."

While speaking to Bay Area reporters, McCaffrey called his friend and former teammate an unbelievable guy and competitor.

"He's been an unbelievable friend of mine," said McCaffrey. "Salt of the earth kind of guy. Just seeing him live out his dream and me live out my dream -- obviously, we're going against each other but it's pretty special and he's a hell of a competitor as well so it will be cool to go up against him."

McCaffrey went on to say that he still talks to Thomas almost every day and considers him to be like another brother.

Thomas never really had an opportunity to tackle McCaffrey at Stanford. He may get that opportunity on Sunday as the two face each other as opponents for the first time. What does Thomas think about the possibility of bringing McCaffrey down for the first time?

"That would be great since I never really had the chance to in practice (at Stanford)," said Thomas. "We wanted to protect him, make sure he's healthy. But if I get the chance, I need to take advantage of it. That'll be a fun thing to talk about in the group chat."

McCaffrey was an important part of Stanford's offense in his two seasons as a starter. As explained by Thomas, head coach David Shaw did not want to take any chances and made McCaffrey off limits to his defenders during practices.

"We wanted to keep Christian healthy, not ding him up at all," said Thomas. "He was already taking so many hits a game, getting a lot of carries. The only problem was Christian would try to come at us and he wanted to hit. That was the competitiveness out of him. He wanted to be ready for Saturdays and he thought part of that was being physical. He'd say, 'C'mon, just give me a little chip.' I'm like, 'I'm not getting in trouble.'"

While Thomas relishes the opportunity to finally hit McCaffrey, the Panthers' star rookie is not looking forward to being tackled by his friend.

"I told him it's the same rule (as at Stanford) so hopefully he believes it," McCaffrey jokingly told Charlotte area reporters.

McCaffrey would prefer to not give Thomas the opportunity to bring him down. Bay Area reporters were also curious to know what the running back thought it might be like being tackled by the defensive lineman.

"I don't know," said McCaffrey. "I'm hoping I don't have to find out. But if it does (happen), I'm sure it won't feel great."

The dynamic and exciting running back averaged over five yards per carry for the Panthers during the preseason. He also caught the football three times for 51 yards. While much of the attention has surrounded Panthers quarterback Cam Newton and his throwing shoulder, which he had surgery on in March to repair a partially torn rotator cuff, Shanahan knows the 49ers must also account for McCaffrey, who promises to be a big part of the Carolina offense.

"I haven't studied him throughout the preseason," Shanahan told Charlotte area reporters on Wednesday. "I know how good of a player he is. I studied him hard coming out of college and I've known him a long time in my life. He's a hell of a person. He's exceptional when it comes to studying the game and having a feel for the game. And his talent is way above most people. I know he's an issue to deal with. You never know. Anytime you have a guy who can be a running back or a receiver on any given play, it causes issues for a defense. I know that will be a challenge for us schematically and athletically to handle him."