When Willis bounced the ceremonial first pitch, the crowd at Citizens Bank Park let the actor hear about it:
Bruce Willis threw the first pitch at tonight's Phillies game. It bounced. The Philly faithful gave him a "warm" reception. https://t.co/EQlBAglbIi
If you want to be charitable to the Phillies fans, it wouldn't be unreasonable to suggest they were chanting "Bruuuuuce" after the pitch.