Hi,
There are already 960+ teams in the UK so the team list would be very long. New teams are appearing weekly so that figure is rising.
Some of those teams just play friendlies at the moment whilst the others will be involved in the leagues.
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Again with Collapsed leagues, the list would be very long especially with multiple league seasons and spread across the world.
Most leagues are in the UK, but there are leagues in Europe and even the USA will be starting up leagues in the next 12 months
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Not sure how the auto complete would work when they need to pick a specific team, in specific league, in specific year, but if that is intuitive then maybe the solution.