Conversation so far:
what is the famous photo of Y. A. Tittle in question?
A photo of a dazed Y. A. Tittle by Morris Berman of the Pittsburgh Post-Gazette is regarded among the most iconic images in American sports and journalism.
what is special about the famous photo of Y. A. Tittle taken by Morris Berman?
Y. A. Tittle, in his 17th and final season, was photographed helmet-less, bloodied and kneeling immediately after having been knocked to the ground.

Question: who was he knocked by?
Self-contained rewrite: who was Y. A. Tittle knocked to the ground by in his 17th and final season?