Interesting idea to put Flash with the Avengers. When the fight starts, I think that Flash would instantly take out Green Arrow and Batman, just leaving the heavy hitters. Wonder Woman's magic weapons would slice through Iron Man's Armor, taking him out of the fight, while Captain America is defeated by Green Lantern. Hulk would take on Superman and Vision would fight Wonder Woman, while Green Lantern chases Flash around, who at the same time would get a few hits on Superman and Wonder Woman. Hulk and Vision would eventually be defeated, leaving just the Flash against Green Lantern, Supermen, and Wonder Woman. Now, depending on what version of the Flash this is, he could very likely win by just stealing their speed and IMPing them all, or the combined force of the other team could be too much for him if he is a weaker version. This battle really just comes down to how powerful the Flash is, so it is basically a coin toss; I can't decide a winner without knowing this.