How did Amos help Auggie and Jack during the nature retreat?

In Wonder, August and Jack are friends who go through different trials but ultimately stick by each other in the face of social stigma. The other kids at August's school ostracize him because he looks different than other people. Julian is the major antagonist, who turns people against Jack and Auggie, but Amos and his friends are part of the popular crowd who constantly bully Jack and Auggie.
When Julian doesn't go to the nature retreat, Amos and his other friends are free from his negative influence. In the most climactic scene of the book (a fight in the woods with the 7th graders), the friends get the assistance and support of Amos, Henry, and Miles, three of the least likely people to help Jack and Auggie. When the 7th graders start making fun of Auggie and physically attack him, it is Amos who steps in and fights to help protect Auggie—seemingly out of the blue.
Amos charges Eddie, one of the 7th graders who attacks Auggie, and it is only with Amos's help that Jack and Auggie can get out relatively unharmed. Afterward, the boys spend time bonding together, and Auggie, now a bit braver, is brought into their friend group:

"Yeah, dudes, thanks," I said, holding my palm up like Jack just had, though I wasn't sure if they'd high-five me, too.
Amos looked at me and nodded. "It was cool how you stood your ground, little dude," he said, high-fiving me.
"Yeah, Auggie," said Miles, high-fiving me, too. "You were like, 'We're littler than you guys' . . ."
"I didn't know what else to say!" I laughed.
"Very cool, said Henry, and he high-fived me too.

This scene is a turning point in the story that leads to Auggie being accepted at school and seen differently, not only by his peers and teachers but by his parents and himself. Auggie grows through this experience; he realizes that he can be brave and fight because of the support from Amos and the others. This is how Amos helps Auggie and Jack.