Now I don't know if anyone has said this but I was rewatching some old Marineford Arc, and something hit me when I saw this scene. Crocodile is over here in the left corner and is standing with the Whitebeard pirates to protect Luffy from Akainu. Also during Impel Down and all through Marineford he talks about killing Whitebeard and then stops and starts helping Luffy it makes no sense why the sudden change. And then he says "Can I truly have been defeated by as weak as this?"Then also Whitebeard make a remark at the beginning when Luffy first gets there, "If Crocodile had not learned his Lesson" when he tried to attack Whitebeard. So why would Whitebeard all of a sudden switch when he has so much hatred for Whitebeard? Then I remembered Crocodile is based on Captain Hook and looked him up then reslized it said he used to be Blackbeard's Boatswain. What is a Boatswain? The boatswain works in a ship's deck department as the foreman of the unlicensed (crew members without a mate's licence) deck crew. Sometimes, the boatswain is also a third or fourth mate. A bosun must be highly skilled in all matters of marlinespike seamanship required for working on deck of a seagoing vessel. The bosun is distinguished from other able seamen by the supervisory roles: planning, scheduling, and assigning work. I also agree with @Joy_Boy Theories on youtube that Oden Kozuki was the 2nd Divison Commander of the crew and after he left nobody was in charge but Blackbeard mostly ran much of it, and one person underneath them could have been Crocodile. Then either after Oden left or during Blackbeard's time either A) Crocodile wanted 2nd Divison Commander position and they wouldn't give it to him or B) something else happened. Caused a commotion between Crocodile and Whitebeard. Causing a Brawl between the 2 and this is how Crocodile lost his arm and got the scar on his face. Which led to the Alabasta and Impel Down stuff that happened. Also making him really angry at Whitebeard which the reason he wanted the Ancient Weapon to destroy Whitebeard's fleet and the Strongest Man Alive who even Old and dying gave Akainu a beating. Also if he knew Oden Kozuki this would give him a reason because maybe he looked up to him to assist Luffy and Marco in the fight at Wano which a lot of people theorize might happen.