Roger Federer and Elmo from Sesame Street seem to disagree on the letters of the alphabet in a Super Bowl ad for ON running shoes.

Watch as Elmo sits in an umpire's chair and debates the two letters found on Federer's On-branded sneakers: Is it 'Q' and 'C' or 'O' and 'N'?

Roger Federer appears alongside Elmo in a new Super Bowl commercial for the running shoe brand, On, that has them debating ...