To summarize the facts of what led up to Nomar being traded:
1) He suffered an injury to his Achilles tendon in spring training. According to Nomar, it happened when he fouled a ball off his heel. But no one else saw it happen, and there were suspicions that the injury wasn't baseball-related.
2) He missed the first 57 games of the season.
3) When he came back, his mobility was noticeably limited. The team did some analysis and concluded that he had become the worst defensive shortstop in the game.
4) He was conspicuously unhappy in the clubhouse. Management was extremely concerned about his attitude and toward the end of July they met with Nomar to find out what was going on with him. The meeting got nowhere.
5) The final straw occurred shortly after this when Nomar informed team trainers and then Francona that he expected he would miss a lot of time in August and September to rehab his injury. Francona called Theo to let him know and Theo talked to Henry, Lucchino and Werner. They were now convinced that Nomar was longer interested in the Red Sox, that all he cared about was looking after himself so he would be healthy in time for free agency.