Joey Bada$$ is only 18, but he's one of the most promising rappers of 2013. Part of the Brooklyn-based hip hop crew Pro Era, Joey's Internet buzz has been building up to a fever pitch since he dropped his 1999 mixtape last summer.

When Mr. Bada$$ and four other members of Pro Era recently stopped by Eminem's Sirius radio channel Shade 45 to freestyle for DJ Kay Slay, it demonstrated pretty clearly what the fan fervor is all about.

For starters, it's worth watching because Bada$$ doesn't really get into a groove at first. "These warm up bars, man," he explains after giving up on his tepid first verse, realizing it isn't going anywhere he's interested in. But when it comes time for him to spit again (3:37 mark), he absolutely owns it. For better or worse, you gotta respect off-the-cuff rhyming—not a ton of rappers actually mess with that anymore.

Keep an eye on Dessy Hinds (second from the right) during this freestyle, too: His flow and voice bring to mind early Jay-Z. Also, shoutout to Kirk Knight (middle) who destroys his second verse on this freestyle. Point is, the whole Pro Era crew demonstrate a command of the game that's eyebrow-raising given their years. Check it out above.