We know Yamato and Ace must’ve fought, as Luffy’s combat style and spirit reminds Yamato of Ace.
![](https://www.opfanpage.com/wp-content/uploads/2020/07/107039246_1758147484343344_9011136604652280307_o.jpg)
That being said, I have a theory as to why they clashed.
![](https://www.opfanpage.com/wp-content/uploads/2020/07/maxresdefault-3-1.jpg)
At this time Ace was not part of Whitebeard’s crew, which means he was probably still hunting Whitebeard to kill him and make a name for himself as an up and comer.
![](https://www.opfanpage.com/wp-content/uploads/2020/07/oiugiu.png)
Maybe Ace expressed this desire to Yamato, that he was in the New World to go after Whitebeard. Yamato, recognized the name Whitebeard from Oden’s journal as a captain and comrade, so in the Oden disguise she perceived Ace as an enemy and they clashed.
![](https://www.opfanpage.com/wp-content/uploads/2020/07/maxresdefault-8-1024x576.jpg)
To Yamato, she was defending Oden’s former captain Newgate. It is what Oden would have done.
*Theory by ahood34