Seems TV ratings for NHK's coverage of the Waseda - Keio yesterday came in at 12.1% for the Kanto region with a high of 16.2% (end of the 8th of the 8th).
In comparison, TV ratings for TV Tokyo's coverage of the Lotte - Chunichi game were at 9.7%. Other shows that competed for an audience at the same time slot:
Akira Ikegami's News Special on TV Asahi - 15.0% (7:00pm - 9:48pm)
Women's World Volleyball on TBS - 14.0% (7:04pm - 9:14pm)
Quiz! Hexagon II on Fuji TV - 13.4% (7:00pm - 7:57pm)
11/5 1:24pm JST UPDATE: TV ratings for the Waseda - Keio game in the Nagoya region was just 7.9% while the Nippon Series game weighed in at 16.2%.