Copyright Question

Hi guys! I'm just new here in YTtalk, I have a question regarding Copyrights, what if someone uploads a short clip of their gaming video and I download it without telling them. The downloaded video is added to my video hightlights. But in my video description, I add their names as a Credits to their video, will the monetization of YouTube will accept the video i made? Thanks!

Also, i wanted to say: this is against YouTube TOS. You are not allowed to download anything off YouTube unless there is an actual button from YouTube allowing you to do this (and youtube only allows you to download your own stuff)