Live streaming ATP tennis is not really live...

Max G.

Quite possibly. With internet streaming, It would make sense to me that that they maintain a 15-ish second "buffer" - because unlike TV, where you can pretty much guarantee that the signal is going to go through, internet connections (for most people) are a lot more spotty. So yeah, I could understand that browsers/media players would keep a "buffer" to keep the video from freezing if the connection goes slow for a little bit.

That's just my guess though. I can't say I've studied the workings of the internet in too much detail, and I don't have this live streaming, so maybe that's just idle speculation..