Shape of wall's deformation wave caused by baseball's impact Clicking through this year's top sports pictures, I stumbled upon this one. I was wondering about the shape the baseball is leaving on the wall.

What phenomenon causes this peculiar shape? Why is it not radially symmetric? My intuition also tells me that the shape should be the solution of some special sort of wave equation (that takes into account the wall's material etc.). But, it looks like something substantially different...
 A: The fabric covering the foam pad has a warp and weave (we can assume.) The fabric can stretch with the warp or the weave but not at a 45 degree angle, called the bias direction in sewing. So, when the ball hits the fabric it causes a wave in the fabric which begins to travel outward like a ripple in water. The wave causes distortion of the fabric as it moves, stretching the fabric if it can. The diamond shape is a map of the speed away from impact that the wave can travel through the fabric. Faster in directions the fabric can be stretched and slower in the directions it cant be. The longer dimension of the diamond is due either to differential in the tension of the fabric in the up and down as opposed to the right to left direction or because the warp direction can stretch more or less than the weave direction. It is a beautiful photo.
A: I guess the shape is defined to a great extent by the structure of the wall, which can be quite complex - for example, the wall can be anisotropic. Another, related guess, which can be more plausible, - the shape can be defined by the vertical and horizontal dimensions of the component of the wall (the boundaries of the components are seen as dark vertical lines and the horizontal edge at the bottom) - the wall is less rigid in the vertical direction, as the external tissue is longer in this direction (it is probably fastened to a frame). So the shape is defined by the solution of a wave equation, but this solution strongly depends on the boundary conditions, on the position of the point of impact with respect to the boundaries, and the tension of the tissue in two directions.
EDIT(12/27/2012) The following article seems extremely relevant:  Int'l J. of Solids and Structures 40 (2003) 6723–6765 , 144.206.159.178/ft/521/198702/5066699.pdf 
