Annoying pop-up on my web browser...

I’ve got this annoying pop-up on my web browser – just comes up outta nowhere- for a game called “League of Angels”. I’m not even a gamer at all. There’s a button to click on the center to play & it usually pops up on 2 tabs at once. Lately it’s been on my Chrome browser & I just close that window but it’s just becoming like a daily occurrence – even more than once a day sometimes. I definitely did NOT do anything to bring it about, haven’t installed any pop up stoppers & don’t even tell my browser to block pop ups.
I’m running a Mac & my Google Chrome browser is Version 44.0.2403.130 (64-bit) [if that matters]. Has anything like this ever happen to you?
So, how do stop this?