In about the middle, the Doctor goes to play in a game of football. When Matt Smith was 16, before he became an actor, he was a football player for Leicester City Football Club, but had to stop due to issues with spondylolysis.
This is the first time in the new series that the Doctor has definitively stated how many incarnations he has had - he tells Craig he is the eleventh.
This episode replaced a script by Neil Gaiman, which was delayed due to budget concerns. This became The Doctor's Wife (2011).
Before the football game, The Doctor pulls on a spare jersey that has a large number 11 on the back. Matt Smith plays the Eleventh Doctor in the series.
This episode was based on a comic strip from Doctor Who Magazine featuring the Tenth Doctor with Rose Tyler and Mickey Smith.