Originally posted by ProFx:

a troll attack my base

Great materials delivered to your doorstep is always welcome
Just stay within the red circle and kite them away from your base. The event lasts couple of minutes so you can a) kill as many as you can within that time or b) kite them away from your base and kill only after the event is ended so that no more trolls spawn in.

There are many different events for your amusement
https://valheim.fandom.com/wiki/Events