When an artist performs their own lyrics over the beat and melody of someone else's song.
This is almost exclusively a trope in Hip Hop and R'n'B.
Like cover songs, the songs that are most often freestyled over are hit songs, of any genre, although mostly (for the reason above), hip-hop, R'n'B and pop songs.
This is not always the case however, and it is not uncommon for a more popular artist to give an unknown a Colbert Bump by freestyling over their song.
This is also related to Battle Rapping, though it's much more competitive than typical freestyling.
The legality of freestyling is in a similar area to the legality of Sampling, which can be viewed at that page.
- Lil Wayne built a lot of his buzz off of this. His Dedication series of mixtapes uses this trope almost exclusively, freestyling over the popular songs whenever the mixtape is released, as does his Da Drought series, and almost every other mixtape he's ever released.
- Kanye West recorded a freestyle over his One-Hit Wonder Rich Boy's "Throw Some Ds", which turned a song about money and cars into a song about breast implants.
- Around a quarter of Drake's mixtape So Far Gone is freestyles, using songs by Jay-Z ("Ignorant Shit"), Kanye West ("Say You Will"), Lykke Li ("Little Bit"), Santogold ("Unstoppable") and Peter Bjorn and John ("Let's Call It Off"). note
- Rick Ross' 2012 mixtape The Black Bah Mitzvah which was entirely composed of freestyles over popular songs at the time - although after Ross had done his freestyle verse, he let every song play out as it originally was, causing lots of Epic Rapping, which for many was divisive.
- Kendrick Lamar freestyled over Kanye West's "Monster" in 2010 and created a brilliant Villain Song out of it.
- Femcee Nitty Scott (who has collaborated with Kendrick Lamar) freestyled over "Monster" and the video of her doing so went viral and kickstarted her career.
- Nicki Minaj has done a few of these, over songs by Jay-Z ("Encore"), [[The Notorious B.I.G]] ("Warning"), and also PTAL's "Boss Ass Bitch".
- Frequent across J Cole's earlier mixtapes, mostly over songs by Kanye West and Jay-Z (notice a theme here?), although also over Cassie's "Must Be Love", Missy Elliot's "Best Friend" and Talib Kweli's "Get By".
- Busta Rhymes does freestyle versions a lot, for instance over such songs as Kendrick Lamar's "Backseat Freestyle" and "Poetic Justice" and Drake's "Best You Ever Had".
- Lupe Fiasco freestyles often on his mixtapes. One, Friend of the People features him subverting the trope slightly, as he freestyles over obscure dance and dubstep instrumentals on it (and also over John Coltrane's A Love Supreme. He also freestyled Que's "OG Bobby Johnson" as "THOT 97".
- The Weeknd did a freestyle version in 2014, freestyling over Lorde's "Royals", Ty Dolla $ign's "Or Nah" and Beyoncé's "Drunk in Love" (although he significantly altered the beat for this one).
- Azealia Banks freestyled over "Harlem Shake" when that song was popular.
- Van Morrison tends to this wnen he does a cover version. His cover of It's All In The Game starts out as a conventional version sticking more-or-less to the official lyrics, but by the end it has diverged so much that on the Into The Music album, the second half of the cover is listed as a seperate track and given a new name (with songwriting credits for the lyrics given to Van).