The companion literary piece to the commissioned artwork by dori-to, "Relaxing on a Saturday Night", the story describes the events both before and after the scene illustrated...a barfight in the "13 Shots Bar" just outside the Canterlot Training Center. This artwork was featured in the "Equestria Daily" Drawfriend.

What happens when you put twenty-eight war ponies in a bar with a gaggle of Griffons?
Do you really need to be told? Not everything in Equestria is magic and friendship.

Link to dori-to's original work.
http://www.deviantart.com/art/Relaxing-On-A-Saturday-Night-483288805