Yaxchilan Lintel 53 Illustration
Lighting can often times inhibit the viewing of the lintel, so this illustration gives a better idea of the ritual happening here. It looks as if Jaguar Shield II is rubbing the feet of a small god, whose foot happens to be a snake's head, onto what might be a large ball game ball. For whatever reason, it may be explained in the glyphs that surround them.
After figuring out the glyphs, they don't seem to be of very much help, other than giving various names for the people in the scene along with their location.