No, they played on her flank when she was asleep, it was on the Apple Bites comics tumblr before it suddenly disappeared when one asked if she was mad when she found out they played on her flank, when she answered... it turned out she hadn't learned that they did yet. (She looked more like Sweetie "Burn" in that image than Sweetie Belle.)
It was cute. And actually raises a question: can a pony get a cutiemark for being a game field? Also, does the 5 Os and 4 Xs on Sweetie flank mean that in Equestrian version O-player makes the first move?