Duel of Harlem

The Battle of Harlem was caused by Abomination attacking Harlem to show his new power. Thaddeus Ross was forced to trust Bruce Banner in order to save Harlem. Bruce fell out of a helicopter, but failed to turn into Hulk before hitting the ground. He transformed into Hulk after a painful fall into a street of concrete, and fought Abomination, starting the battle.

Background
Toward New York City, Bruce Banner and Betty Ross were making small stops along the way and both were located by Kathleen Sparr. They went to Empire State University, Manhattan, to meet Banner's "Mr. Blue" Internet friend, Dr. Samuel Sterns, a cellular biologist. Accompanying Sterns to his lab, Banner and Betty learned that Sterns had developed a possible antidote that might reverse Banner's transformations after their occurrence, but was unlikely to prevent future ones, while an overdose could possibly kill him. Despite the risks, Banner agreed to test Sterns' antidote, and submitted to a test. The experiment worked, and exhilarated by the success, Sterns revealed that he had synthesized Banner's blood sample into a large supply with the intention of using it to enhance the human condition to the next evolutionary level. Appalled by what his colleague had done and fearful of the Hulk's power falling into the wrong hands, Banner attempted to convince Sterns to destroy the blood, but was then shot with a tranquilizer dart by one of General Ross's snipers.

Emil Blonsky made Dr. Sterns infuse him with gamma radiation. When he did, the mix of the Super Soldier Serum and gamma radiation transformed Blonsky into a creature known as Abomination. Abomination threw Dr. Sterns into a container of Bruce's blood, which leaked into a scar in Stern's forehead, which made his brain grow and gave him a higher than genius level intellect.

Battle
As both Bruce and Betty were taken into custody, Blonsky, now a hideous titan known as Abomination began rampaging through the city in a bid to draw out the Hulk. Banner, realizing that he was the only one who could stop the Abomination, he was able to convince General Ross to release him. He jumped out of a helicopter, counting on the fall triggering a transformation and Hulk focusing on Blonsky as an obvious threat as opposed to him unleashing more random destruction.

Banner's plan succeeded, and after the violent, pitched battle, he defeated the Abomination by strangling him with a huge chain. Poised to deliver a final blow, he was stopped in the act of killing by the intervention of Betty, leaving the scene with the army in hot pursuit.

Aftermath
After the battle, S.H.I.E.L.D. found Serns and took him to a S.H.I.E.L.D. facility and called the project "Project: Mr. Blue".

After turned, Banner fled north to Canada. Thirty-one days on the run, he had found himself a secluded place to rest, and there he began practicing a new technique of initiating his transformation in a controlled manner.