Some years ago, a young Clark Kent enters Gotham City (which he holds about the least amount of regard for possible) in search for an interview with Bruce Wayne. Bruce seems to be in that period of his life where he doesn't want anyone to know he's alive, looking like complete shit, and watching on a park bench, as a young kid of a Middle East descent gets picked on, until Clark steps in. Clark then turns his attention to Bruce, who is surprised to be identified, asking if he has any comment on the recent murders of Wayne Enterprises employees in Metropolis. Although Bruce eventually admits to being himself, he has no comment other than pointing out to Clark that Gotham is quite different than Metropolis.
Naturally, Bruce goes to Metropolis to investigate, where he finds a not herself Catwoman attacking the one Wayne Enterprises employee who refused to relocate for the night. Selina barely reacts to any of Bruce's attacks, acting as if she was possessed. The target of the would be execution manages to scramble around his apartment and activate some experimental Wayne Tech security robots he shouldn't have... Or at least attempts to, but Bruce takes the controls, and orders them to apprehend Catwoman.
At this point, Superman shows up, and with everyone being generally unfamiliar with each other, all hell breaks loose, as Bruce and Clark start to fight... Well, Bruce mostly just tries to avoid, best he can. The fight leaves the man's apartment, and while Bruce and Clark are separated for a moment, a spirit looking being manifests out of Catwoman, seemingly pleased with the fight at hand. When Bruce and Clark charge at each other, the impact is met with a very specific "BOOM" and the next thing Clark knows, he's in Smallville.
Clark ends up on the ground, and finds Batman again, only this time Batman calls him by name, has a different costume, and doesn't seem all too interested on continuing the fight... To just clear up everything, it's because Clark is now on Earth 2, and this is the Batman of that Earth. Clark, not knowing any different, just continues to fight, but is stopped in his tracks when Batman brings up a kryptonite shield around him.
Clark manages to discard of the small piece of kryptonite Batman had on him, and while Batman thinks Clark is settled down... not so much, and the beating continues for real this time... That is until Jonathan Kent shows up, horrified in his son's (from another Earth) actions.