Just as a backstop in baseball prevents a ball from leaving the playing field, a backstop to an offering insures that the funds required by the firm are raised.
Backstopping can cost companies large fees when participating in a rights offering. Similar to an underwriter, the backstop purchaser takes on the risk of issuing new securities and is paid a premium for compensation. For example, when Berkshire Hathaway acted as a backstop purchaser for USG Corporation, it earned a non-refundable fee of $67 million for the service.
Investment dictionary. Academic. 2012.