Nam Y. Huh/AP
The Steelers had reportedly agreed to stand in the locker room tunnel together during the anthem, according to ESPN's Jeremy Fowler, but Villanueva, an Army veteran, stood outside of it, by himself, with his hand over his heart.
Villanueva, who served three terms in Afghanistan, did not comment after the game.
According to Fowler, the move caught some Steelers by surprise, not because of the gesture, but because it had not been agreed upon. Steelers coach Mike Tomlim told reporters after the game that he only wanted his team to be together 100%.
"Many of them felt like something needed to be done," Tomlin said (via Fox News' Greg Norman). "I asked those guys to discuss it and whatever they discussed that we have 100 percent participation or we do nothing. They discussed it for an appropriate length of time and they couldn't come to an understanding, so they chose to remove themselves from it."
Tomlin added: "Like I said, I was looking for 100 percent participation. We were gonna be respectful of our football team."
James Harrison told Penn Live's Jacob Klinger: "We thought we were all in attention with the same agreement, obviously. But I guess we weren't."
Not all Steelers players were bothered or surprised by Villanueva's decision, however. According to Fowler, Steelers players respect Villanueva for his service. Guard David DeCastro said he wishes there was a different form of protest for Villanueva's sake:
"Al is a unique circumstance, what he's been through, some of the things he's talked about before ... I've got a lot of respect for Al. I wish there was a different way to do this thing. We've got some people who look at the national anthem as patriotism, soldiers, all the stuff that it means, and obviously, people are upset, and I understand that. I just wish both sides understand that they want the right thing, but doing it through the national anthem, I wish there was a different way."
Fans apparently appreciated Villanueva's gesture. According to ESPN's Darren Rovell, by Monday, Villanueva was the top-selling jersey in the entire NFL.
Last year, Villanueva said he didn't agree with Colin Kaepernick's decision to kneel during the national anthem (via ESPN).
"I don't know if the most effective way is to sit down during the national anthem with a country that's providing you freedom, providing you $16 million a year ... when there are black minorities that are dying in Iraq and Afghanistan for less than $20,000 a year. It's his decision. Obviously he has brought up the issue in a great way. But I think if he encourages other players or other people in the stands to sit down, it's going to send the wrong message."
Villanueva also said at the time that he'd be willing to "hold hands" with Kaepernick and discuss any issues.
This past August, the Washington Post's Adam Kilgore asked Villanueva if his thoughts had changed now that Kaepernick was unemployed, and his tone changed slightly.
"I absolutely think he was very brave for what he did," Villanueva said. "I don't necessarily agree with the fact he kneeled down for the national anthem. I also don't understand every single circumstance going on in his life. I do it because of all the veterans, all the soldiers I served with."
Villanueva had said that he couldn't fully comprehend Kaepernick remaining unsigned because other players kneeled during the anthem and remained on a team and that he didn't know about Kaepernick's abilities as a quarterback. He said there's no law saying players have to respect the flag.
"I think it's a personal decision. I think it's respect. But if you don't want to be respectful toward the American flag, I don't think there's any law that says you have to be respectful."
It's unclear where national anthem protests go from here or what the Steelers plan to do next week. Ben Roethlisberger has already said he regrets how the Steelers chose to remain in the locker room on Sunday. However, regardless of their decision, it doesn't appear that Villanueva will change his mind.