A bizarre Marvel Studios rule says that Sebastian Stan's appearance as Bucky Barnes in Captain America: Civil War is considered a cameo. Following his debut in 2011's Captain America: The First Avenger, Bucky became instrumental in the overall arc of Steve Rogers, aka Captain America (Chris Evans), throughout his time in the massive superhero franchise. Though he started out as a supporting figure in Steve's story, Bucky has since stepped into the spotlight for his own Disney+ series The Falcon and the Winter Soldier opposite Anthony Mackie's Sam Wilson.
It was in 2016's Captain America: Civil War where Bucky truly seemed to come into his own as he became the key to Steve's true moral compass as a defender of freedom and as a loyal friend. Following the death of the Wakandan king, T'Chaka (John Kani), law enforcement, the Avengers, and Black Panther (Chadwick Boseman) were hot on Bucky's trail as they assumed he was the culprit. Bucky spent much of his time in Captain America: Civil War as an unfortunate fugitive, but he also reached a major turning point in his fight against Hydra's Winter Soldier brainwashing. Stan was a pivotal member of the Civil War cast.
Related: Why Bucky Feels Pain In His Robotic Winter Soldier Arm
However, per THR, a Marvel Studios rule says that Stan's crucial role in Captain America: Civil War amounted to a cameo appearance. According to this rule, if a character's screen time results in less than fifteen percent of the film's total runtime, then the actor's role will be considered a cameo. Stan's total screen time in Captain America: Civil War was only 22 minutes, meaning that his appearance constitutes a cameo per Marvel Studios' rules. This is essentially so Marvel can limit what it pays
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