It's probably 20% of every Northwestern crowd (if we want to get picky, that's why our Nebraska game had 8,000 more fans than the UTSA game), but that's always been the case.
Here's the best way to say it, I think:
In 2003, we bottomed out to 1-11. Attendance dropped to an average of 50,961. That same season, Northwestern went bowling and averaged 28,763 fans. "LOL", I said. "They'll always bring in half our crowd."
In 2019, 3-9 Northwestern brought in 37,736 fans per game, while 6-6 Illinois attracted 36,587 per game.