There are a lot of meanings related to たたき台 (as noted by the comments and posts above.)
In one case (from your picture posted above,) たたき台 actually means something like "a pounding stand" for baseball gloves. (Along with a たたき台, there is also another tool used when pounding baseball gloves like this, called a たたき棒; the actual glove-hitting tool.)
When you buy a typical baseball glove, it is usually made out of some sort of leather. Leather usually requires some sort of maintenance from time to time (and especially before a glove, in this case, is first used.)
One type of glove maintenance is the art of "creating a pocket" so that a baseball fielder can more-easily catch a fly-ball... or field a ground ball... during a game of baseball.
The following (commercial) website describes what the process of "creating a pocket" can look like:
http://bba.co.jp/kakou-teire_shinka.html (see step 7)