Complex sentence: Seeing Oboro as the easiest way out, Saemon hurled Yashamaru's cleaver at her but missed when Tenzen knocked her out of the way and took the blade on his arm, creating an opening which granted Saemon the oppurtunity to throw the battle scroll out the door.
Split into simpler sentences: Seeing Oboro as the easiest way out, Saemon hurled Yashamaru's cleaver at her, but missed when Tenzen knocked her out of the way and took the blade on his arm. The resulting opening gave Saemon the oppurtunity to throw the battle scroll out the door.