Here is a video clip of free-agent center Shaquille O'Neal(notes) singing along to a Justin Bieber song (or, at least, what I think is a Justin Bieber song; this is the first of Justin Bieber I've ever heard) at what appears to be a sound check before a Bieber concert in Phoenix.
Yes, there are fans there, but oftentimes artists will charge their fans three or four times the price of a ticket to get the "privilege" of attending the sound check of the performer they've already bought the ticket to see. (The sound check is 90 percent filled with snare drum level measuring, and about .0125 percent filled with the star in question actually singing.) Usually a limited meet-and-greet will be tossed in there, along with some of that artist's swag (T-shirts, key chains).
This is what my level of intelligence regarding this particular subject extends to. As any other insight into Bieber, or Shaq's interest in him? You're on your own.
Anyway, apparently Shaq paid that price, and it's my guess that he charmed his way into borrowing the front-of-house-sound-guy's mic, and sang along to a Bieber song.
Here you go, basketball fans: