Obviously Superman, like most comic superheroes, has a perverse enjoyment of violence and fighting. He just limits on what he will do, because he was raised by God fearing farm folk. Assumption behind this is that the two are fighting for some reason. And if that's started, unless Superman is smart enough to recognize that Hulk will weaken if Supes just leaves him alone (he isn't), then Hulk will continue to be angry for the duration of their fight, and will remain as Hulk.
Okay, so next step. Get the Hulk up in the sky where Superman would be hovering. You see the pattern here? Every way this fight plays out the only way Hulk wins is to cripple Superman in some way. Don't blame me, blame the creators.