Rubber
From PLANTFACTS.OSU.EDU
1. The pitcher's plate in baseball, located on top of the pitcher's mound.

The picture shows a pitcher's plate rubber being positioned.
Source: http://www.ics.uci.edu/~eppstein/pix/ivy/tigers/PitchersPlate.html
1. The pitcher's plate in baseball, located on top of the pitcher's mound.

The picture shows a pitcher's plate rubber being positioned.
Source: http://www.ics.uci.edu/~eppstein/pix/ivy/tigers/PitchersPlate.html