Song that's played during training scene with kid?

I'm talking about the song in the beginning of this video: https://www.youtube.com/watch?v=cuz-dKIl_BI
I've been searching everywhere. Nobody on Youtube seems to know it, it's not on the soundtrack, Shazam etc. don't know it, Google doesn't help...
So I was hoping maybe somebody on here knows the name of it.