Take a good look at the broken area. I have seen a few broken cranks on duty rated engines. Most often they are an existing crack that finally let go. Look for dissimilarities on the surface of the break in surface finish and color.
Timing can influence crank shaft cracks too. Many older castings were not as good as today and many a small internal crack got through but most won't break in these duty rated stuff.
I doubt a prop strike could break a crank but it would do the rest of the drive train no good.
Dave Neptune
