So I went to Riverwood right, and all of the sudden everyone's balls to the walls attacking me, I tried sheathing my weapon but it doesn't work! How do I yield?

Only thing I could find out is when you sheath your weapon a guard might accept a yield.

Edit: try waiting for 3 days somewhere then come back.

Yielding doesn't always convince the enemy / attacker to stop their attack, just as when the enemy yields you can still choose to stick a blade in them, or set them on fire.

Just sheath your weapon, but that doesn't seem to work all the time. Not sure if it's a bug or if it has to with the opponent's agressiveness level (if you attacked them, as opposed to guards reacting to stealing or bounty)

no yield just run....wait a few days and then come back. People always have the tendency to jump in front of my sword or fire spell or fist in a brawl and then the whole town attacks. I never yield to the enemy anymore they just get up and attack half the time anyway.

It's not a bug.

To yield, sheath your weapon, if it doesn't work, it means you can't yield (the aggression level toward you from that enemy is too high to allow for a yield).