Baseball Question

Last night on Sunday Night Baseball Joe Morgan was critical of Boston's Mike Cameron turning for the dogout when the second baseman was circling under his infield fly with a runner on first and one out. In light of the infield fly rule, which was never mentioned, I wondered why they were critical of Cameron. And I also wondered why they did not mention the infield fly rule. And I wondered why the infield fly rule was not called by the umpire. I TIVO'd the segment and then Googled the infield fly rule. Can you define the infield fly rule?