Noah "Panda Bear" Lennox told Pitchfork Media that this song, "is really an encouragement song for my brother who was having kind of a rough time at the time I was writing the song. That's what the song is about, for me at least."
Panda Bear explained to Pitchfork Media how this tune came together: "The very first version of the song was just me improvising singing over a couple guitar chords, I can't remember what effects I was running through with an acoustic guitar, but I was playing to a Moodymann sample. I'd taken a little piece of a song of his as a rhythm to make a song to. I didn't really want to use that as the final thing, but the first version of the song was that. It was really house-y sounding and I came across a weird Brazilian drum school sample that eventually became the thing we used as the foundation of the song. The guitar chords kind of came second after the rhythmic part of the song and then the lyrics were the very last thing, which is kind of typical for me - the lyrics are always the last part of the puzzle of the song."
Ed Droste of the band Grizzly Bear posted a leaked MP3 of this song on his blog, adding that it was the band's favorite song since "Leaf House" (from Animal Collective's 2004 album Sung Tong's). This prompted a take-down notice from Web Sheriff, a company employed by Animal Collective's record label Domino and some pre-release publicity for Merriweather Post Pavilion.
Dave "Avey Tare" Portner explained to Pitchfork why they decided to make this the closing song on Merriweather Post Pavilion: "A lot of stuff goes into the thought process for us. The history of our band, that goes into it. Like, what have we already done in terms of putting out a record? Have we had the slow, mellow closer or the epic closer? There was a time when I thought 'Brother Sport' could be the first song on the record because it's so positive. But Brian ('Geologist' Weltz) thought, 'Oh, it's too powerful, it'll kill it. The rest of it will just be this weird mellower kind of thing.' We closed our set so much with 'Brother Sport' that it just seemed like the natural way to end. I had my doubts, personally. For a while at least. The recorded version is different from what we do live, and there are a lot of songs that I thought could end up being the last song, but it ended up with "Brother Sport". We were all happy."