Boars are frightened by you being too close, fire being too close, and monsters being too close. Once they have been alerted to your presence they will try to attack until you get out of their perception radius for a long enough period of time for them to calm down (which is quite a bit farther than their alert radius).

The boar's alert radius is 6 meters. The easy way to solve your problem is to build an animal enclosure (ideally a covered barn of some type) that is at least 6 meters by 6 meters. Fence the barn's yard in with stakes walls or rails that are at least 6 meters away from the barn and then build work benches to make sure the area the boars are in is covered so that monsters can't spawn in (you can hide the workbench in the ceiling of the barn) and keep your self and all sources of fire (and light) outside your stake walls or rails until the boars are tamed.