Here are some of the methods i use, to play Youtube in the background. 

**Through Browser**
Using Chrome or Mozilla it doesn't matter, all you need to log into the site and click on the 3dots and select  the option for *desktop site*  when the video plays, you can run it  in the background and do some other tasks. 
 It can even be played in the lockscreen. 

**Through Apps** 
There are apps in the playstore, which are floating pop up ones, which can be used that. it will come handy when doing the multi tasking 
*[Floating tube]( https://play.google.com/store/apps/details?id=com.sarvopari.anytime.floatingtubeplayer&hl=en)
*[Free stream for youtube: stream](https://play.google.com/store/apps/details?id=com.djit.apps.stream&hl=en)
Due to some copyright issues they had to remove the play from the lockscreen, which sucks. 

*Or using 3rd party apps*  
There are Few MODed apps thats let you play in the background and perform much better without the ads 
but it requires **ROOT**
If your device is Rooted then no doubt you must be using the moded ones. 

For those who dint perfomed ROOT on their Device, you can google "*OG youtube*" . It does the required function as we need. Last time i used, it was buggy hope it sorted out. 
Good thing about the app it can be played in background even on lockscreen and download functionality. 


Got any other methods? if you do then please let me know in the comments.