There were multiple reports at the time that Bard asked to become a starter; the Red sox did not have to acquiesce to that request, but it sure didn't seem at the time that they went to him and told him he was going to become one.
And he was already showing signs of losing it in September 2011. He blew multiple games that month. In 11 games and 11 innings, he went 0-3 with 3 blown saves and a 10.64 ERA, walking more batters that one month than he had the rest of the season combined. Now, whether that was due to overwork (he ended up pitching in 70 games that year, losing it or some combination of the two we will never know, but it was awful and contributed a lot to the Sox collapse that season.