Complex sentence: Lannan was called up again as part of the Nationals' 2012 September call-ups, filling the starting rotation job of Stephen Strasburg after Strasburg was shut down in early September.
Split into simpler sentences: Lannan was called up again as part of the Nationals' 2012 September call-ups. He is slated to fill the starting rotation job of Stephen Strasburg after he was shut down in early September.