PAJAMA GAME's behind-the-scenes arrangement concerning the creative team is described in Kevin Winkler’s book “BIG DEAL: Bob Fosse and Dance in the American Musical.” It seems that Hal Prince wanted to hire Fosse (who was still in his 20s and had never choreographed a Broadway show), but was concerned about his lack of experience. So Robbins came on as a backup, with the understanding that he'd be credited as co-director. The aforementioned list which details Robbins' contributions to the show is also reproduced here.
It’s a terrific book by the way, and should answer any questions anyone might have related to Fosse’s career.
