Assertion: warning track | /r/HasProperty | formalized by mlb
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text: Early attempts at warning tracks included sloped fields to give outfielders a heads-up that the wall was coming (sounds like a bad idea as they sped up into it), but it wasn't until 1949 that the warning track was formalized by MLB, which required cinder paths or something other than grass in all parks, 10 feet from the walls.