The sash window in Mrs Hammond's living room, as seen from the inside (presumably a studio set), has been fitted back-to-front and upside-down. The curved "horns" (moulded wood) are at the top of the lower, inside (sliding) pane, when they should be at the bottom of the upper, outside (fixed) pane.
In reality, it would have taken years of training for Frank Machin to become a professional rugby player.
When Machin is leaving the ground (to go to the dentists) the shadow of the boom mic operator is cast on the door as he walks to the car.