I have a hard time believing that somebody praised as one of the most gifted Sharingan users (Shisui) against prodigy amoung the naturaly battle elite Uchihas (Itachi) had a fight completly in the dark, silent, unknown to anybody, and the one left standing as the winner seemed completly unharmed the next day. I believe there is more to Shisui's story that we haven't been told (not a conspiricy or anything just some details that were left out). Either that or Shisui was hyped up a lot and was actually a punk, which I doubt.