My follower is attacking someone. Can I get him/her to stop?

You could use a calm spell to get them to stop fighting and fast travel away. They should chill out after a few in-game days have passed without them seeing each other. Alternatively, if you have an entrance to a different cell nearby (indoors -> outdoors, one dungeon level -> different dungeon level, etc), you could try going through and fast traveling before the NPC can give chase. The safest bet is to reload to an earlier save, though.

If its a human take all their stuff and then wabbajack until they turn into an animal or transform into another thing. It'll last for a few seconds and then they'll act like nothing happened, give back their stuff and yeah.

I know becuase Marcurio always uses his chainlightning and he hits my dog which they start fighting. Wabbajack the best.