Spoiler Thread: Avengers Infinity War

I think y'all are to focused on what you know about comic book Hulk and not focused enough on realities of MCU Hulk.

MCU Hulk just got the *** whipping of his lifetime from Thanos. Something he never experienced before. Now he can likely grow into a bigger rage monster and fight Thanos (who would still win due to the stones), but for the first time in his existance, he feels fear, he feels doubt, and he's not sure if he can beat him. We know from Ragnorck that Hulk in the MCU isn't just a rage monster, but a complex being with many emotions.

In that context, it makes perfect sense that he would do what he did (basically hide). He'll no doubt overcome that, but it will take something happening that propels him to overcome his fear. Black Widow's life being in danger would make perfect sense.

It would take a lot for the Hulk to get to the levels of power he does in the comics like World Breaker Hulk or Heart of the Monster but that's the power level he would need to get to in order to even try to go toe to toe with Thanos even for a little bit. With Hulk getting the beat down at the beginning of the movie you know he's due to have a time to shine in part 2.

I think you are on to something about what you said about Black Widow. In the World War Hulk series his wife dies and a lot of others he cares about and it's enough for him mega rage and beat the brakes off all the X-Men, New Avengers, Mighty Avengers, Fantastic Four, and others without breaking a sweat. He literally snaps Colossus arms like twigs and slaps the Juggernaut out the way like a gnat at a BBQ. If something happens to Black Widow or possibly even news about Betty Ross "dying" when Thanos snapped his fingers at the end of the movie it might take him to World Breaker levels.

Thanos' gauntlet looks to be out of commission at the end of the movie so him utilizing the power of the stones could be out of the question which would give the Hulk the opportunity to square off with him if he's angry enough. Maybe Thor uses the bifrost and transports himself, Thanos, and Hulk off world somewhere at the end and Hulk absorbs enough gamma somehow like in Heart of the Monster and has the ability to literally destroy planets.... there, Thor and Hulk, maybe Captain Marvel wipe the floor with Thanos and all is well again.

The last paragraph is super far fetched but I think something is definitely going to get the Hulk angry enough in part 2 to get him to power levels we have yet to see in these MCU movies.