Do your little cousins go running wildly around the house every time they're visiting? Then they're uncontrolled — they aren't being restrained by anyone or anything.
Anything uncontrolled isn't kept in check or held back. An uncontrolled scream is intense, because you're not trying to tamp it down. An uncontrolled balloon has blown loose and is flying around with no one holding its string. And scientifically speaking, an uncontrolled study or experiment doesn't use a so-called "control group," which is used for comparison and makes the study more valid.