In the settings for the light that is casting the shadows check the Shadow blur radius setting. 

I get quite sharp shadows using a setting of 2
multiple lights will of course affect how crisp the shadows are .

you can also check that the shadow camera is covering only your scene, too big an area, too low a resolution on the shadow map and you get fuzzy shadows.

You can also switch to ray traced shadows.

Also make sure your shadow color is set to black