At approximately 3:05 PM EE was walking from the plant to the C-9 Belt area when EE passed the Oversize chute a 1 1/2 -2 inch rock bounced out of the screen 2 chute and hit EE on the left thumb. A splint was placed on EE's left thumb to minimize movement. Restrictions given from clinic were no typing, pushing, pulling and to wear splint.