It was a physical AND mental error, If Kinsler knew his footing wasn't right, he cannot make that throw, the only way Muncy could possibly score on that play is if Kinsler throws the ball way. The risk was far too great to risk the throw, especially with a catcher playing 1B. If he had just fallen down and couldn't make the throw, okay, bad luck, but the decision to still make the throw was just dumb. You cannot do that.