No it can't be square. Although in theory it could be 90 x 90 metres, the rules state that the touchline must be longer than the goal line.
Can A Football Pitch Be Square?
Yes it can, the longest regulation size for the the goal sides of the pitch is 90m and the shortest regulation size for the touch lines is 90m so it can be 90x90 but thats the only time it could be
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