Freestyle in rap
The idea of freestyle certainly isn't new. I can only imagine that the idea of spontaneous poetry has been around as long as the idea of poetry itself. Historically, however, poetry went through a long dark period lasting for several thousand years, when people thought that poetry was meant to be written. While people still sang songs, singing doesn't lend itself to lyrical improvisation to the same extent that spoken words do. Only with the advent of hip hop music in the later part of the last century did freestyle become popular again. With the advent of slam poetry, perhaps freestyle will gain currency in other forms of poetry, but for now it is tied down to hip-hop, at least by people's perceptions.
Freestyle recordings
Despite talk in The Source and amongst hip-hop purists at the coffee shop, who recount glory days of freestyle throwdowns in the South Bronx, recordings of freestyles don't play a prominent part in most hip-hop albums that are released. Partly this is due to the fact that many new hip-hop stars are chosen for image and don't actually have much talent. Partly this is because if someone is going to go to the trouble of spending some money on studio time, they are going to be putting their best work forward, and not something they are making up off the top of their head. Even the best freestylers have awkward breaks and pauses in their raps, and even great freestyles that sound great live often don't translate well into recordings. If you do want to find great freestyles by people like Krs-One and the Wu Tang Clan, looking online is one of the only places to do it.
With that being said, all the rappers worth their salt today picked up the skills they did have, and many of their best lyrics, while doing a freestyle.
Making your own freestyle
Is it possible to freestyle yourself? Of course. I have read elsewhere that you will only embarass yourself by doing so. (This involves some racist notions I will deal with below). If you freestyle, will you sound just like Method Man or Mos Def? Probably not. If you go out to play baseball in a sandlot, will it look like a major league game? Probably not. But as long as you get something from it, you can freestyle.
The basic technique of freestyle is to make sentences and make sure they rhyme, which is extremely easy. At first, the largest problem is not coming up with the right rhyming word before you reach the end of the sentence.
Later on, coming up with the right words is a problem. A freestyler should start out by coming up with a list of common one syllable words and find ways to string them together. Most of these ways will seem either cliched or totally absurd and disjointed. Don't worry, just keep on working on it.
Before long, the freestyler should be able to string together words realtively easily. Hopefully, they are also avoiding using too much set pattern (personally, I still rely on the phrase "I'm the one...") and what they think of as hip-hop slang. Perhaps people with quick imaginations can even think of ways to freestyle about a single topic without too many wild digressions to save the rhyme. This phase is actually a hard step to get over, because the freestyler can know what she is going to say, and thus her rhymes often tend to end up in an evenly matched, singsong pattern, which both limits creativity and isn't that fun to listen to after about two minutes.
To break out of this, the practicioner should start throwing in weird three syllable words in the middle of the line, practice rhyming a single rhyme until it is exhausted, use alliterartion, use words that barely rhyme or don't rhyme at all...all of these will cause the rhymer to sound totally disjointed and awkward. This might seem bad at first, but it is actually much preferable to rhyming "bad...sad...mad...glad...boy...toy...joy...soy" for hours at a time.
Along with the verbal side, another side must be practiced: overcoming stage fright. While freestyling is fun while you are by yourself, it really comes alive when you have an audience, or other people who are freestyling. Personally, I started out with my sister, and then later moved on to my friends, and only later got to freestyle in front of strangers (and that was in the dark and in front of slightly inebriated people). Ways to overcome shyness are slightly out of the scope of this node, but at some point they will need to be done.
If you can learn to freestyle in multiple rhyme patterns in front of strangers, and perhaps even doing it topically, you will have picked up a valuable tool, although perhaps not one that you can use everyday. From here, it is just a matter of practicing your rhythm and vocabulary, as well as perhaps your stage presence.
Why people have semi-racist ideas about freestyle
For many people, if you asked them to freestyle, and they deigned to humor you, they would probably explode outwards with a line of profanity and yo. Since openly mocking black culture is not acceptable in America, mocking hip-hop or "urban" culture is the outlet for people's racist notions.
It goes much deeper than that: "White America", (which could be defined a number of ways), draws its cultural identity from the concept of abstraction. Part of this concept of abstraction entails the idea that words reflect ideas, usually ideas that have to do with instrumental\hedonistic thinking, with the goal being apotheosis. Freestyling, by the fact that the words are coming naturally and often have no justification but themselves, presents an Oroboric worldview, with things being their own justification. In many ways, this use of language resembles what Heidegger was referring to when he said: "Language does not belong to people, but people to language". This use of language reflects the misconception that "White America" has of "Black America"'s nature, a misconception caused by them taking "Black America" to be the reflection of their own misconceptions of themselves. "Black America" has built in justifications, and any crime or desire it has can be justified without question by its own Ouroboric nature. As opposed to the nature of "White America", that doesn't exist in "the world", but is an abstraction riding above it, "Black America" merely exists in the world, and cannot leave that place. It is this ouroboric nature of desire that "White America" both envies and fears. And thus, someone freestyling, letting their words carry themselves, is something that has to be persecuted, or at least mocked.