aplications are send to background randomly

i have about every 15 minutes that the aplication i am using is send to the background for no reason (i cant see a program running). for instance when i am watching youtube video in fullscreen the video gets back to the small payer. it does this when a program start but when it happens every 15 minutes i cant see a program starting.
and when i am gaming the games get paused/minimalised too. wat program does this? and if no one knows is there a way in the settings to turn off that programs are send to back when a new program starts?

The main question would be why are programs started when you are running a game ?
Or did I misunderstand you there ?
On the other side when this happens every 15 minutes regardless of which application is running, then there might be a programm you installed responsible for this.
15 minutes is btw. also the time for the screensaver to turn on I guess. So maybe its the screensaver. Try turning it off.

it is not exactly 15 minutes
sometimes i dont have it for an hour and sometimes it just happens every 30 seconds.
in window behavior settings i set focus stealing prevention to extreme and it till happens.