Crosby wasn't on the bill for the festival, so his appearance was completely unexpected by the crowd.The two musicians tackled CSN's 1969 "Wooden Ships," as well as "Ohio," the famous protest song penned by Neil Young in response to 1970's Kent State shootings.

Isbell, who is well-known for his outspoken stance on politics—and has performed "Ohio" at his concerts in previous years—spurred the audience to join in on a loud and furious chant of the song's "Four dead in Ohio" outro.

The 2018 Newport Folk Festival, which runs through July 30, welcomed a variety of musicians from different genres. Country standouts Margo Price, Sturgill Simpson, Willie Nelson's son Lukas Nelson (with his band Promise of the Real) and Isbell's wife Amanda Shires were also on the bill.

Isbell scored his first-ever CMA Awards nomination for Album of the Year for his latest album, The Nashville Sound in 2017. He lost to Chris Stapleton, who took the honor for his From A Room, Vol. 1.

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