Rug pull scams "pumping up" a new project, nonfungible token (NFT) or coin to get funding. After the scammers get the money, they disappear with it. The coding for these investments prevents people from selling the bitcoin after purchase, so investors are left with a valueless investment.
It happens in crypto all of the time. Only about 10% of crypto projects are legit. Three projects that I like are RVN and 0xMR because they had no ICO and all coins were fairly mined and ICP, which is backed by the World Economic Forum.