I see a lot of people asking about this

You can in Nokia Lumia

I've got an iPhone and I've done it before. You turn your phone off, then on again and press play.

Wait, there are ads on youtube? I think I should turn off my adblock sometimes...

I've played YouTube with my screen off before. I don't even have to be using safari, I can be playing a game while listening to YouTube.

if you use your web browser on your phone and go to YouTube.com you can

with an iphone if you don't have the youtube app you can start playing the song on youtube's mobile website and then lock the screen, bring the lock screen up and swipe up and press play :)

Android users can download the app PVSTAR+ from the Google Play Store to watch YouTube videos with their screen off.

This is partially wrong.

Or you could just click play when you swipe up...

I'm gonna buy one of these little blue frogs. They're so damn smart.

This is the best thing. All my mind is clear.

This comment makes me feel like God has given me a nudge?

iphone can do it, i do it everyday