It'll be like kong and godzilla.
One is in a rage, so the more even-minded has to step up from a far-away home.
For this case, Superman would act all evil for no reason, presumably from the red kryptonite that Lex Luthor acquired. As superman becomes a tyrant, Lex Luthor scours the earth for the Dragonballs.
Goku from another planet training with Whis gets the news, goes back to earth to fight Superman.
Superman easily beats Goku in the first round.
Goku gets a new form or zenkai boost, goes for round two.
Goku is still the underdog in the fight but manages to help Superman break free from the influence of the Red Kryptonite.
Just in the nick of time, when Lex Luthor unleashes his newest creation, some kryptonian/saiyan clone created by the dragonballs, then souped up with whatever lex tech he could muster.
Two team up and it show that both need each other in the fight.
Once its all over, Superman and Goku part ways as friends/friendly rivals.