As the Fastest Man Alive, the Flash has one of the Justice League's most versatile power sets, and one of his strongest moves is so powerful that it could take out Superman himself. DC Comics' speedsters are capable of reaching unprecedented levels of speed, but fans often forget how dangerous Flash's abilities actually are. Early on in their seminal JLA run, Grant Morrison and Howard Porter cemented the Flash's place among the world's greatest and most powerful heroes.
Out of all the Scarlet Speedsters, Wally West is the fastest Flash. With his unique connection to the Speed Force, he was the first to discover many of the abilities every Flash now employs. And in JLA #3, one of those moves - something nicknamed the Infinite Mass Punch - managed to take down a Superman-level threat.
Early in the series, a mysterious group of new heroes called the Hyperclan arrive on Earth to supplant the Justice League. The world's greatest heroes are immediately suspicious, and rightfully so as the Hyperclan are later revealed to be villainous White Martians. When the JLA splits into teams and investigates the Hyperclan's bases in JLA #2, Green Lantern Kyle Rayner and the Flash head to the Gobi Desert, where they’re confronted by three Hyperclan warriors, including the speedster Züm. Moving at superhuman speed, Wally intercepts the threat before he can get his hands on Kyle. The pair race around the planet so quickly that their footprints set the ground ablaze, battling it out every step of the way. Recognizing Züm’s military training, Wally realizes he has to think as fast as he moves and begins to lap his opponent. Moving at lightspeed, the Flash's mass increases towards infinity, and he puts it all into one punch that sends Züm to another continent at escape velocity as Wally thinks, "Maybe he is as tough as the Man of Steel. But packing the mass I mentioned - I’m sure he felt that."
Putting down a White Martian is no easy feat, as all of them are on a level of power rivaling the Martian Manhunter: the one hero Superman is afraid to face. While the JLA eventually triumph over the Hyperclan when they learn their weaknesses, these invaders were still strong enough to incapacitate most of the League in their initial confrontations. The fact that the Flash managed to take down even one of these foes single-handedly while also managing to race around the entire world says a lot for the dexterity of Wally's abilities and his mastery over them.
The Flash is undoubtedly faster than Superman, but this maneuver also gives him the superstrength needed to hurt the Last Son of Krypton. While Superman is incredibly fast, he can't keep up with Wally. If the Flash really chose to come at Superman as fast as he could, Kal-El couldn't stop him, which is even more significant when Wally's speed allows him to hit with such incredible power (not to mention his ability to scour the world for Kryptonite while Superman is still recovering.)
The Speed Force allows the Flash Family to do some pretty amazing things, and taking out Superman-level opponents is definitely one of them. The Flash’s speed may be his primary power, but it's instances like these that demonstrate just how dangerous DC Comics' Fastest Man Alive really is. With power like the 'Infinite Mass Punch' at his disposal, Superman and the Justice League should just be glad Flash is on their side.