For 1B Umpire John Tumpane, working his first career ALCS, this meant a quick adjustment from an expected out/safe timing call to a potential pulled foot situation, and the umpire dutifully shifted his focus to Choi's footwork to determine whether or not the fielder maintained contact with the bag.
In order to do this, Tumpane adjusted his position to form the keyhole angle (or wedge or view) required to best officiate this play and see potential separation (or daylight) between foot and base.
In this case, Tumpane confirmed that Choi had successfully keep his cleat in contact with the base and therefore ruled Bregman out, a called confirmed following Replay Review initiated by a Manager's Challenge.
Video as follows:
Video as follows: