Atlanta Hawks Organist -- I Got Hired Off Craigslist ... And Now I'm Cool With 2 Chainz

The Atlanta Hawks' best defense against LeBron James during home games might be their badass organist who keeps the fans turnt up, and has 2 Chainz and Ludacris hanging on every note.

Sir Foster's become a breakout star during the Hawks' playoff run by busting out renditions of songs by Chris Brown, Outkast, Lady Gaga, Bon Jovi ... pretty much every genre of popular music. He tells TMZ Sports it's all thanks to Craigslist.

Foster says he landed his dream job when "the team put out a Craigslist ad for an organist. I had zero experience playing sporting events, but I figured, 'I have nothing to do today,' so I went."

He nailed that audition 6 years ago -- and now that the Hawks are dominating deep into the playoffs, he's getting national recognition, and local celebs dig him too. "I've gotten a lot of support from artists like Ludacris, 2 Chainz, Pastor Troy and The Dream."

Foster says the key to his success is staying away from traditional (aka boring) stadium music -- "I play the songs people in Atlanta like to listen to."

He's smart too ... during last night's game, Foster busted out Lil B's "Wonton Soup." Always good to give props to The Based God.