The protest took place at Monday's MLB game against the Miami Marlins.
The two men who snuck the banner into the park were escorted out by security who said they'd return the flag, but a police officer ended up confiscating the personal property.
See footage from the view of the Trump supporters below.
The man behind the stunt, Dion Cini, has made headlines in the past for similar demonstrations.
Last month, Cini unfurled a "Trump Won, Save America" banner over the second deck during a Yankees and Blue Jays doubleheader, and provoked mixed reactions from fans, who could be heard cheering and booing.
In Feburary, Cini was attacked by security at a NYC ice rink for flying a large Trump flag at a skating rink operated by the president's organization.