Billie Joe Armstrong turned a quiet corner of Petco Park into a full-on Comic-Con moment yesterday, when he and fellow Green Day members rolled a Nimrods-branded ice-cream truck into Gallagher Square for a blink-and-you-missed-it promo stunt. Armstrong climbed onto the truck roof, knocked out an acoustic version of "Basket Case" and flung ice cream and T-shirts into the crowd, while fans and curious passersby hustled over from around the Gaslamp Quarter. Young star Mason Thames and Jenna Fischer were spotted near the action, and within minutes, the surprise set was over, leaving the plaza buzzing.
Surprise set in Gallagher Square
As reported by NBC 7 San Diego, Armstrong used the Nimrods-covered ice-cream truck as his stage, strumming through "Basket Case" before pivoting to giveaway mode. Station footage shows him playing a few bars, then turning the truck into a merch cannon, tossing sweets and shirts to fans clustered in front of the makeshift stage. NBC 7 also identified Mason Thames and Jenna Fischer among those watching the quick pop-up.
A movie push: 'Nimrods' and Green Day
The Petco Park stunt was timed to promote Nimrods, a coming-of-age comedy that Green Day produced with Live Nation Studios, according to a Live Nation Newsroom release. According to the film's official site, Nimrods is scheduled to open Aug. 14 and stars Mason Thames in the lead, with Jenna Fischer and McKenna Grace in key roles.
Fans, lines and freebies
NBC 7 San Diego noted that social media posts from the scene showed a steady line at the novelty truck, with one account pegging the queue at roughly 120 people waiting for ice cream and swag. Short clips of Armstrong's rooftop performance made the rounds online, while TheWrap shared photos of Mason Thames and Jenna Fischer taking in the mini-set, underscoring that this was more of a blink-and-you-miss-it fan moment than a full Green Day show.
Mason Thames and Jenna Fisher watch on as Green Day gives a surprise performance at #SDCC for their movie #Nimrods pic.twitter.com/4XdtVoKj8S
— TheWrap (@TheWrap) July 24, 2026
Why it mattered locally
Gallagher Square, the grassy public plaza at Petco Park, is a regular home for fan activations and community gatherings, so it was a natural landing spot for a Comic-Con-timed pop-up. Petco Park's official ballpark guide describes Gallagher Square as a space for concerts, screenings and public events, and Friday's quick hit was another reminder that the ballpark doubles as a downtown staging ground when Comic-Con takes over the neighborhood.
Where to see it
Tickets and showtimes for Nimrods are listed on the film's official site, nimrodsmovie2026.com, with the movie opening in U.S. theaters on Aug. 14. For anyone who did not catch the Gallagher Square surprise, the pop-up served as a very Comic-Con reminder that sometimes the biggest moments happen in the spaces that are supposed to be just a park.
