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
Bruce Banner and Betty Ross where trying to get an antidote for Bruce's gamma radiation condition, so they went to Samuel Sterns, who Bruce had been working with indirectly for more than a year through computer messaging.Bruce tested the antidote, which seemed to work, but only temporarily. Thaddeus Ross an his team of soldiers captured Bruce and Betty.

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 then 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.

At the same time, the S.H.I.E.L.D. agent Natasha Romanoff found Sterns and saw his mutation. When he tried to convince her to help him evade the authorities, she shot him in the leg and called a clean-up team.

Aftermath
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 rather than supressing it.

Sterns was later taken to a S.H.I.E.L.D. facility where he became part of "Project: Mr. Blue".