Question: During which part of the game is the middle line used?
About the article "Squash (sport)", section "The court".

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An initial grid of dots are drawn; a square of 4x4 dots, with a rectangle of 4x3 added to each side.
The initial cross is outlined in some versions of the game.
During each turn, draw a straight line that is exactly five "dots" long, such that: No part of the new line can retrace any portion of a previously drawn line.
In the outlined version, the line can continue an existing line (they must not overlap).
Exactly one of the five dots covered by the new line is missing from the grid before the line is drawn.
This missing dot (which can be at either end of the new line, or somewhere in the middle) is also drawn during the turn.
In the only outlined version, if no new dot is needed when drawing the line, the dot may be saved and can be used in later turns.
In other words, make a five-segment line from four dots, and draw in the fifth (unless it is saved to draw two dots in later turns). 
Further plans have been launched, in particular the section of the Nordland Line from Trondheim to Steinkjer, which is part of the Trøndelag Commuter Rail, and the Meråker Line, which connects to the electrified Middle Line in Sweden. 
The pitch is a rectangle, 70m long by 32m wide divided into:  the in game (""în joc"") area, which is 60x32m  the batting zone (""zona de bătaie"") - 5m long - delimited from the in game area by the batting line  the back zone (""zona de fund"") - a 5m long safe zone during a run - delimited from the in game area by the back line The attacking side player that has commenced a run will have to cross the following four lines in order:  the start line (the left side of the batting line)  the arrival line (the left side of the back line)  the return line (the right side of the back line)  the escape line (the right side of the batting line) The in game area is further split into the advance and return triangles and squares.
At the intersection of the lines inside the game area and the pitch limits or other lines within the game area, there are circles which determine the positions of the midfielders (""mijlocaşi"") and side players (""mărginaşi"").
The 1m and 3m semicircles are used for batting and serving.
A waiting line is drawn for attacking players to wait their turn to bat. 
The game has been historically popular in Persia, Muslim countries, and among Babylonian Jews.
The name "nardshir" comes from the Persian "nard" (Wooden block) and "shir" (lion) referring to the two type of pieces used in play.
A common legend associates the game with the founder of the Sassanian dynasty, Ardshir.
The oldest known reference to the game is thought to be a passage in the Talmud, although some claim it refers to the Greek game Kubeia.
Another early reference is to be found in the Middle Persian romance of Chatrang-namak (written between the 7th and 9th centuries) which attributes the invention of the game to Bozorgmehr.
By the 17th century the game was played in Georgia under the name of nardi, and by the 19th century it was being played by the Kalmucks (who called it narr).
During most part of the 20th century both Georgia and Kalmucks were parts of USSR, so now the game is played in Russia and other ex-USSR countries under the name of nardy (нарды). 
A game of rugby league consists of two forty-minute halves, played by two teams on a rectangular grass field of 120 metres in length and 58–68 metres in width depending on the individual ground.
In the middle of the field is the 50 metre "halfway" line.
Each side of the field, on either side of the 50 metre line, is identical.
10 metres from the 50 metre line is the 40 metre line, followed by the 30, 20, 10 metre and goal or 'try' lines.
This makes up 100 metres of field that is used for general play.
At the middle of each goal line is a set of goal posts in the shape of the letter 'H', used for point scoring from kicks (drop goals, penalty goals and conversions).
Six to twelve metres beyond each goal-line is the dead ball line.
The area between these two lines is called the in-goal area, and varies from field to field.
The dead ball lines and the touch-lines (side lines) make up the boundary of the field of play.
If the ball (or any part of the body of a player in possession of the ball) touches the ground on or beyond any of these lines, the ball is said to be "dead" and play must be restarted.