When Bridget tapes over a video Kerry was using for a school project, Paul insists that Bridget cooperate on Kerry's replacement project. Kerry's theme: how the "beautiful" Bridget uses her looks to get her way. This annoys Bridget because she thinks it makes her look shallow (it does). So she takes up tennis---to give her "depth."
Spoilers ahead. Coverage follows the scope labeled below.
Complete story — includes the ending
Kerry devotes her school video project to Bridget to illustrate the hypocrisy that life is much easier for the beautiful people. But when Bridget discovers that the video makes her look shallow, she takes Paul's advice to enrich her life by taking up tennis again, and ends up with a broken nose. Bob and Mike Bryan, the No. 3-ranked tennis team in the world, make a cameo appearance on the tennis court.