The family of five, including children James, 8, Betty, 6, and Inez, 3 posed at the stadium, with Mr Reynolds, 46, holding the newborn.
Mr Reynolds’s team went on to beat York City 3-0 in the Vanarama National League. The co-owner of the club, Rob McElhenney, also attended the game, according to the Daily Mail.
Mr Reynolds and Mr McElhenney bought the Welsh club in 2020.
On Sunday 12 February, the A Simple Favor star shared a photo of herself on Instagram, in which she could be seen without her baby bump.
“Puppy Bowl Sunday 2023. Been busy,” she wrote in the caption of the Instagram post, which showed her standing with Mr Reynolds and his mother Tammy.
The pregnancy update came after Ms Lively revealed that she was pregnant with her and Mr Reynolds’ fourth child in September when she debuted her baby bump on the red carpet during the 10th Annual Forbes Power Women’s Summit.
In the comments under her latest post, fans and followers also hinted at the news that Ms Lively has given birth.
“Epic post! For all the reasons!!!” Deadpool creator Rob Liefeld wrote, while one fan added: “The baby is here!”
“When did you have the baby?!” someone else asked.
Mr Reynolds previously spoke of his excitement over Ms Lively’s fourth pregnancy during an interview with Entertainment Tonight.
“I’m very excited,” he said, before joking: “We’d have to be. You know, you’d have to be a moron to do this four times if you didn’t like it. It’s gonna be nuts, but we’re very excited.”
During Super Bowl Sunday, Lively also debuted a new commercial for her ginger beer brand Betty Buzz. However, rather than air the ad during the Super Bowl, Lively shared the commercial during the Puppy Bowl.