Overwatch teaser points to new rolling hero

Another teaser has just been posted to the Overwatch Twitter account, following up on the cryptic alleyway image that went up last week. This time, a large ball of some sort rolls through the frame.

What does it all mean? Is Samus Aran joining the Overwatch cast with her morph ball power? Sonic, is that you rolling around at the speed of sound?

Nah, couldn't be. We think the Boston Uprising is on the right track: