How The Flash Would Defeat Each Member Of The Justice League
1. Superman
It’s been established that The Flash can run far faster than Superman and any time the Metropolis Marvel beat the Scarlet Speedster was just Barry holding back for charity. But he has no chance of matching Clark’s strength, heat vision, or flight abilities. Of all the members of the League, dealing with Superman would be the most difficult for the Flash.
The most obvious means of defeating Kal-El would be through Kryptonite or red solar radiation. Once he removes the yellow solar radiation from Clark’s body, it would merely take one super-speed punch to bring Superman down. The kryptonite would be the quickest but potentially the most deadly. Presumably, Barry doesn’t want to kill the Man of Steel, so trapping him in a room with red solar lights would rob him of his strength and leave Supes vulnerable.
Another way would be to overwhelm Superman with rescues. The Flash is fast enough to create a series of “natural” disasters that would require Superman’s attention for long enough for Barry to achieve his objective, assuming it isn’t to simply beat Clark. Convincing the Boy Scout that he is needed off-planet to save someone would achieve the same goal.