When I was speaking to fans who were at the Beatles concert in Cincinnati on August 21, 1966, most of them recalled one thing: Paul McCartney did not act like his normal happy, thumb aloft self during the concert. George was more into the show than Paul.
First thing they noticed that Paul fell way behind the other Beatles when walking onto the field. The other three bounced on down the field, at times waving to the crowd and got up on the stage. Meanwhile, Paul lagged behind with his bass up to his ear, trying to tune the instrument. He was having trouble getting it to sound right. The rain from the night before was over and in it's place was a hot, humid day. That humidity had caused Paul's bass to lose tune quickly.
When Paul made it up onto the stage and plugged into the Beatles Super Amp, he complained to Mal that it sounded like a "fuzz box." Mal just shrugged his shoulders. What more could he do? The amps had gotten soaked the night before and he did his best to dry it out.
Besides all the stress with the instruments and amps, Paul just wasn't feeling well. He was throwing up in the hotel room the previous night. It was hot--he was sick for whatever reason and the last thing Paul wanted to do was perform. However, he was there and went through the show. It just was a disappointment to Paul fans in the audience.