In the Avengers movie, when Banner's in flying fortress, he is angered and transforms into Hulk. Black Widow happens to be next to him. Both are on same team. But he attacks her. Then Thor. He becomes futile to everyone on the ship.  
But later on, in the fight against Chitauri troops, Hulk is very comfortably self-controlled. 
Why is that?  
The only thing I could think of is, its been many days (a year) since Hulk had gotten angry, so he couldn't control himself.  
But thats lame to be so puny when he was compared to Stephen Hawking is smartness.