Which fractures tend to occur first when a pane of glass is struck?

The correct answer is radial fractures.  

Glass bends in reaction to any force, which is imparted on anyone on its surfaces; when the elasticity limit of a glass is reached, the glass fractures. The infiltration of a general window glass by a projectile, whether it is a stone or a bullet, generates a familiar pattern of fracture in which cracks both encircle the hole and radiate outward.  

The radiating lines are suitably called radial fractures, and the circular lines are known as concentric fractures. A radial fracture refers to a crack in a glass, which elongates externally like the spoke of a wheel from the point at which the glass was struck.