Complex sentence: Witnesses gave highly conflicting testimony of what occurred and who started the fight, but what is not in doubt is that Hookes fell to the ground, hitting his head in the process, and going into cardiac arrest.
Split into simpler sentences: Witnesses gave highly conflicting testimony of what occurred and who started the fight. What is not in doubt is that Hookes fell to the ground, hitting his head in the process, and going into cardiac arrest.