Complex sentence: Avex Trax director Yasuyuki Tomita and Hamasaki had talked about a "baseball theme song" and while she was convinced by it, Tomita later reconsidered the idea and scrapped it.
Split into simpler sentences: Avex Trax director Yasuyuki Tomita and Hamasaki had discussed having a song with a baseball theme. While she was convinced by his idea, Tomita later reconsidered the idea and scrapped it.