While there are six heroes who have gone by the name “The Flash”, for the purposes of comparison here, we will focus on Barry Allen, the current Flash and Justice League member before the events of Dark Crisis #1. Among his many nicknames, he is called “The Fastest Man Alive”, and he certainly lives up to that claim.
Of his many other skills, the Flash’s reaction time has been measured to be faster than an attosecond. The attosecond is one quintillionth of a second. This allows him to think, plan and act before most beings even observe the situation. His speed is so great that he can run on surfaces that have no solid properties, like water, clouds, laser blasts, and once, photons. Barry can manipulate his own body’s molecules and pass harmlessly through solid objects, travel into other dimensions, through time, or into the Speed Force itself.
Given the nature of his powers and how quickly he can formulate a plan and execute it, it seems logical that the Flash could make short work of the roster of the Justice League and incapacitate them all with relative ease.
The highly moral CSI would need a very good reason to move against his teammates, of course, because some of the ways he’ll have to take them down might hurt more than their egos.
10. Green Arrow And Black Canary
Between this loud-mouthed, liberal bowman and this disciplined fighter, the Flash is wisely worried about facing Black Canary the most out of these two. Not in a physical fight, of course; Dinah’s good and is able to perceive a nanosecond attack thanks to sparring with Wonder Woman, but unless she gets in a lucky shot, Flash could easily dodge her blows. It’s her other power that concerns him.
It is the Black Canary’s Canary Cry that worries Barry. Able to reach 300 decibels, which is double the sound of a jet engine taking off, the Cry is enough to make human ears bleed even if they aren’t in the blast area, and would be enough to stop the Flash in his tracks. A quick throat strike or rendering Dinah unconscious would eliminate that problem, but Dinah is rarely alone.
Oliver, for all his bravado, is just a very skilled man with a bow and arrow. Remove those and Barry eliminates most of the problem. Although any archer worth his salt has arrowheads hidden throughout his costume, so removing them or striping him to his underwear will be necessary. Other than his mouth and his chili, which should be considered a deadly weapon, the Emerald Archer’s most unusual "weapon" lately has been being the right guy in the right place at the right time to, as he puts it, “save the damn day”.
Sadly, that didn’t work out so well for him in the events of the Dark Crisis. Regardless, there is no specific way for the Flash to fight that until it happens.