Ener-Core, Inc. (ENCR)

[js9909]

https://en.wikipedia.org/wiki/Greenshoe

To manage this situation, the underwriters initially oversell ("short") the offering to clients by an additional 15% of the offering size (in this example, 1.15 million shares). When the offering is priced and those 1.15 million shares are "effective" (become eligible for public trading), the underwriters are able to support and stabilize the offering price bid (also known as the "syndicate bid") by buying back the extra 15% of shares (150,000 shares in this example) in the market at or below the offer price. The underwriters can do this without the market risk of being "long" this extra 15% of shares in their own account, as they are simply "covering" (closing out) their short position.


Keep in mind this refers to high demand but the same concept applies to propping a stock.