After Mustipher filled in for an injured Cody Whitehair in Week 7, coach Matt Nagy raved about his intelligence. Offensive coordinator Bill Lazor called him "impressive" after meeting Mustipher over the summer.
Running back David Montgomery appreciates how Mustipher and guard Alex Bars are always there to pick him up off the ground at the end of plays.
"He came in the same year as me," said Montgomery. "You'd think he has been in the league 10, 11, 12 years the way he coaches out there. He just takes charge. He's the general on the line, and [the other linemen] believe and buy in."
Mustipher has started the last three games at center, with Whitehair, a Pro Bowler in 2018, moving to guard. Offensive line coach Juan Castillo said there hasn't been any drop-off.
"They're both grading out the same," said Castillo. "I think Sam is a starting center in this league."
Castillo has known Mustipher since the center played high school football with one of Castillo's sons in Maryland. Castillo remembers Mustipher coming to the Baltimore Ravens facility to work out.
Though Mustipher has spoken about the stigma of being an undrafted player, his new offensive line coach just remembered him as a top-flight, Notre Dame-bound recruit.
Though Mustipher's path to starting included a full year on the Bears practice squad, he's not surprised to be anchoring an NFL offensive line.
"That's always been a goal of mine," said Mustipher, "and really it wasn't necessarily a shock for me because that's the way I prepare, that's the position that I've prepared to put myself in. But I was given an opportunity, earned an opportunity, however you want to put it, and I feel like right now, all I can do is keep making the most of that opportunity."
The opportunity hasn't come in a straight line upward. Mustipher started in Week 8 against the New Orleans Saints, only to miss the next two games with a knee injury.
"When you get that first opportunity, that first start, and you get injured, [it] wasn't the best feeling in the world," said Mustipher. "But the same way that I attack being a professional football player every week was the same way I attacked the recovery."
Mustipher credits the Bears training staff with aiding his quick recovery and now views the early setback as just another challenge he has overcome.
Mustipher's college experience at Notre Dame required him to earn playing time alongside a bevy of future NFL linemen, including Ronnie Staley, Mike McGlinchey, Quentin Nelson, Nick Martin and current teammate Bars.
The connection has come in handy. Martin, who plays for the Houston Texans, acted as a mentor to Mustipher early in his college career. Nelson, who plays for the Colts, stayed in the Chicago area in the offseason to train with Mustipher and Bars.
Even playing at a high level, including a run to the 2018 College Football Playoff, Mustipher has had to adjust to the sheer talent he faces every week.
"There's a lot of differences," said Mustipher. "Moes and Joes, not Xs and Os. There's a lot of good Moes and Joes in the NFL. There's a lot of talented people, from coaching staffs to players themselves. I think that's a big adjustment from college football, and just getting used to that and learning every week and gaining experience is very important for me."
Perhaps most crucial for Mustipher is the respect of his teammates. Lazor recalls the entire team's positive reaction when Mustipher's name was called out earlier in the season.
"One of the greatest compliments I can give Sam," said Lazor, "is that when his name is brought up in front of the group—how do I put it?—the reaction of the team, offensive and defensive players, the cheer that came up almost took me back."