Chicago Fire has captivated audiences for over a decade, drawing viewers into the high-stakes world of Firehouse 51 with its compelling blend of intense rescues, intricate character arcs, and the unwavering bond among its firefighters. Much of the show’s enduring appeal lies not just in its dramatic narratives but also in the palpable chemistry and genuine relationships among its cast members. These off-screen connections often translate into the authenticity that viewers cherish, creating a sense of a true family within the fictional firehouse. David Eigenberg, who portrays the beloved veteran firefighter Christopher Herrmann, recently offered fans a rare glimpse behind the scenes, revealing deeply personal moments and playful antics that shape the show’s unique spirit, particularly around the poignant departure of original cast member Jesse Spencer.

Eigenberg’s insights, shared during an interview, shed light on the unscripted moments that have become an integral part of the cast’s journey together. When discussing what Chicago Fire consistently “gets right,” Eigenberg pointed to the genuine camaraderie that exists among the actors, emphasizing that while much of their shared experience makes it to the screen, some of the most heartfelt interactions remain private. One such tradition, affectionately dubbed “water bottle ball,” originated in the very first season. During long days of outdoor shoots, several cast members would gather, link arms, and playfully kick an empty water bottle around, attempting to pass it through each other’s legs. Described by Eigenberg as “stupid” and brief, this simple, spontaneous game became a cherished ritual—a small moment of levity and connection amidst the demanding production schedule.

This seemingly trivial game took on profound significance during one of the show’s most emotional moments: the farewell of Jesse Spencer, who played Captain Matthew Casey, in Season 10. Casey’s departure marked a significant turning point for Chicago Fire, as Spencer had been a central figure since the pilot, embodying the moral compass and leadership of Firehouse 51. His character’s decision to move to Oregon to care for the sons of his late friend Andy Darden, while a fitting and heroic arc, left a considerable void for both his on-screen family and loyal viewers.

As the cast prepared for Casey’s emotional send-off scene, which called for a group hug, the “water bottle ball” tradition spontaneously re-emerged. Eigenberg recounted how, as the actors embraced in a genuine show of affection, someone instinctively dropped a water bottle into their midst, and they began to kick it around. This unplanned moment, filled with shared laughter and “little tears,” was a raw and authentic expression of their sadness and affection for Spencer. It was a private, unscripted goodbye that perfectly encapsulated the deep bonds forged over a decade of working together. Though it never made it into the televised episode, Eigenberg acknowledged that while it was a beautiful, personal moment for the cast, it “didn’t belong in the show,” preserving the intended narrative gravity of Casey’s departure for the audience. This distinction highlights the unique relationship between the actors’ real-life friendships and the fictional world they inhabit, with the former providing the bedrock for the latter’s emotional depth.

Beyond the poignant goodbyes, Eigenberg also revealed the lighthearted, often boisterous, atmosphere that pervades the set. He described the cast as having a “low-grade sense of humor” and admitted to a playful “physical aggressiveness” behind the scenes. This isn’t about conflict, but rather a testament to their comfort and familial bond, where wrestling and friendly roughhousing can break out, especially when clad in heavy bunker gear. This energetic camaraderie extends to all members, regardless of gender, creating an inclusive and robust environment.

A prime example of this dynamic came with the arrival of Miranda Rae Mayo, who joined the cast as Stella Kidd in Season 4. Her quick integration into the playful rough-and-tumble of the set immediately signaled her fit within the Firehouse 51 family. Eigenberg fondly recalled Mayo’s very first encounter with this boisterous tradition: “When she first showed up, she threw me to the ground and jumped on top of me and did some other stuff to me, and I looked up and everyone, we were laughing so hard. She started it. She buried me and I told everybody, I said, ‘She fits in.’” This anecdote perfectly illustrates how the show’s cast not only works together but genuinely plays together, fostering a sense of belonging and mutual respect that enriches their on-screen performances. Mayo’s character, Stella Kidd, has since risen through the ranks to become Truck’s lieutenant, mirroring her strong presence and leadership within the show’s ensemble. Her journey from a new recruit to a pivotal leader within Firehouse 51 is a testament to both her character’s development and Mayo’s successful integration into the core cast dynamic.

The One Chicago universe, a sprawling tapestry woven by legendary producer Dick Wolf, thrives on interconnectedness, with characters frequently crossing over between Chicago Fire, Chicago P.D., and Chicago Med. This shared universe allows for rich narrative possibilities and deepens the audience’s investment in the characters’ extended lives. When asked about a character he’d like to see cross over to Fire, Eigenberg immediately named Marlyne Barrett’s character, Maggie Lockwood, the formidable charge nurse from Chicago Med. His reasoning revealed another layer of the actors’ creative input and desire to flesh out their characters’ histories.

Eigenberg shared an intriguing tidbit about a past attempt to subtly hint at a pre-existing connection between Herrmann and Maggie. During a pilot for one of the crossover events, Eigenberg played a scene with Barrett where he deliberately imbued Herrmann with a familiar, almost flirtatious, demeanor towards Maggie. His intention was to suggest that Herrmann and Maggie “had a thing back in the day” before he met his wife, Cindy (played by Robyn Coffin), implying a history given Cindy is younger than Herrmann. While the subtle acting choice didn’t make the final cut—producers deemed it wouldn’t “play in the crossover pilot”—it highlights the actors’ deep understanding of their characters and their enthusiasm for exploring rich, untold backstories within the expansive One Chicago canon. These unscripted ideas and character nuances, even if ultimately unused, are a testament to the cast’s commitment to building a believable and intricate world for their audience.

The longevity and profound emotional impact of Chicago Fire are undoubtedly fueled by these behind-the-scenes realities. The true friendships, the shared laughter, the spontaneous traditions like “water bottle ball,” and the genuine tears shed during a cast member’s farewell are the invisible threads that bind the actors together. This authentic camaraderie translates directly into the on-screen chemistry that viewers have come to love, making Firehouse 51 feel less like a set and more like a second home. The dedication of actors like David Eigenberg to their roles, combined with their personal investment in the ensemble, ensures that Chicago Fire remains a show where the lines between character and actor, and between a fictional family and a real one, beautifully blur, reinforcing its status as a beloved staple of television drama.