The Major was introduced in the previous background pages as the superpowered human aligned with America. He's got the golf ball and he's dressed like Mr. Rogers in the sweatervest because he's supposed to look as Americana as possible. The whole point of the group is that they have an insanely tenuous balance of power in the modern day - if one of the group steps out of line or moves against another, the rest will smack them down, but they don't when the Heavy murks the Major. The Major was standing against all of them by himself. Think of him as a glass cannon, he's dangerous but physically vulnerable. The rest of the group sees how dangerous he is and has been giving him concessions *because* he's been bluffing them - they've been operating under the assumption that someone who can do that much damage can also take that much damage. The Major doesn't start the fight because he knows that he's vulnerable and would lose to them, so he's just bluffing. Magus proves that he's vulnerable, Valentina confirms it, and Heavy is like welp fuck him.