YOU SAID:

I was killing my best friend in the ocean when someone started a food fight

INTO JAPANESE

私が海で親友を殺していたとき、誰かが食べ物の喧嘩を始めた

BACK INTO ENGLISH

Someone started a food fight while I was killing my best friend at sea

INTO JAPANESE

私が海で親友を殺している間に誰かが食べ物の戦いを始めた

BACK INTO ENGLISH

Someone started a food fight while I was killing my best friend at sea