The Flash is so fast he could end this fight before Batman's neurons fire a single signal.
Batman has prep plans for the Flash, and in certain storylines they've been somewhat effective. But in a straight fight, the Flash's speed makes this a non-contest.
The Flash can think, move, and react at speeds that make light look slow. Before Batman can reach for a batarang, Barry has already disarmed him, tied his shoelaces together, and written 'you lose' on his forehead in permanent marker. The speed gap between Flash and Batman isn't a gap โ it's a chasm.
Batman's contingency plan for the Flash typically involves traps that exploit Barry's need to run โ frictionless surfaces, absolute zero environments, speed-dampening technology. But these require preparation and environmental control. In a random encounter, Batman has no chance.
Batman has developed contingency plans specifically for defeating Flash. He's the greatest tactical mind in DC and could set traps designed to negate superspeed. Batman also has speed-dampening tech and cryo weapons that could theoretically slow Flash down.
The Flash moves faster than the speed of light. He can vibrate through solid matter. He can steal kinetic energy from objects. Before Batman's brain can send the signal to 'dodge,' Flash has already won. Speed Force makes this matchup unfair at a fundamental physics level.
The Flash wins instantly in any scenario without specific Batman prep. The speed differential is so extreme that Batman can't even perceive the Flash in combat, let alone react to him. With elaborate prep, Batman has a slim chance โ but that's true of almost any matchup with Batman prep.
Batman also fights
The Flash also fights