Read more about H.A.M.M.E.R. at: Wikipedia

Official Site: Marvel Comics

H.A.M.M.E.R. is a fictional espionage and law-enforcement agency in the Marvel Comics Universe led by Norman Osborn. The organization is formed in Secret Invasion #8 to replace S.H.I.E.L.D.. The organization plays a large part in Marvel's "Dark Reign" and Siege events.

What "H.A.M.M.E.R." stands for, if indeed it stands for anything at all, has not been revealed. In Dark Avengers #1, Osborn told Victoria Hand that it does stand for something, and when she asked what it stands for, he told her to "get on that for him". Also, in the Captain America: Reborn Prelude, when Sin, who is captured by H.A.M.M.E.R, asks what it stands for, the agent present says that it's classified and she does not have a security clearance.

The ramifications of the alien Skrull' invasion of Earth forced a massive restructuring of the United States' defense network. At the time, the country's primary peace keeping agency was S.H.I.E.L.D., led by civilian industrialist Tony Stark, aka, Iron Man. Because the Skrulls were able to compromise S.H.I.E.L.D.'s StarkTech technology, it was decided that S.H.I.E.L.D. was no longer an effective organization and Tony Stark was personally held accountable for the entire Skrull invasion. In the wake of this controversy, Thunderbolts leader Norman Osborn manipulated the U.S. government into allowing him to serve as director of a replacement agency called H.A.M.M.E.R. Under Osborn's leadership, H.A.M.M.E.R. had administrative control over the entire Fifty State Initiative.

As the director H.A.M.M.E.R., one of Osborn's first initiatives was to issue warrants for the arrest of former S.H.I.E.L.D. director Tony Stark and deputy director Maria Hill. Moreover, Osborn wanted access to the database containing the identities of every hero registered under the Superhuman Registration Act. To prevent Osborn from getting his hands on such vital information, Tony Stark took measures to erase all known resources containing this sensitive information, including his own mind.

H.A.M.M.E.R. has not been a contender in any CBUB matches.