Saw it again last night. Not sure what the hell is going on with Hulk. If he was scared, why not just take over then run away. Why hide inside Banner and let him fight?
The only thing I can think of is that Marvel is setting up a major redemption for the Hulk, he's there Superman. I can only imagine a MAJOR butt whipping dished out to Thanos by the Hulk. Something so grand people stand up and cheer.