Wednesday, May 15, 2019

Ask UEFL - HR Replay Stands Due to Parallax

Red Sox batter Michael Chavis' home run over the Green Monster and out of Fenway Park Tuesday night resulted in a "call stands" outcome, upholding 3B Umpire David Rackley's HR call in favor of Boston following a Rockies-requested Replay Review.

We received an Ask the UEFL question about the Replay Official's decision to uphold Rackley's call of "fair ball/HR" all while a camera angle from the stands up along the first baseline suggested the batted ball may have been foul.

What happened here and why did this call stand?

Replay Review lost sight of a high fly ball.
Analysis: This is a perfect example of parallax proving unreliable, if not deceptive. As the attached video analysis demonstrates, the camera angle well to the right of the left field foul line/third baseline extended has a habit of making any batted ball in flight look less fair than the ball actually is (and vice versa for a camera angle from the third-base dugout, paired with a batted ball near the right field line).

To counteract the parallax deception, baseball relies on another law of physics related to vision: if the ball crosses in front of the foul pole, the ball is therefore closer to the viewer than the pole at the point at which it crosses the pole. Ordinarily, for a viewer watching the ball/pole interaction from the playing field (as an umpire or player would), this is a shortcut to say that a ball crossing in front of the pole and leaving the playing field in flight is a fair ball and home run.

Conversely, a ball crossing behind the pole suggests it is farther away from the viewer than the pole at the point of intersection, which would suggest a foul ball.

Parallax proves certain replays unreliable.
Why the Call Stood: For this particular play, Chavis' home run was hit so high in the air that the foul pole frame of reference did not apply to this play, as far as Replay Review was concerned. Because the pole and ball interaction did not appear in any video replay, the Replay Official could not conclusively determine what the ball's location was as it left the playing field (e.g., when it crossed the plane separating the field from the spectator area, as signified by the foul pole).

Due to his angle from the playing field surface up the left field line, 3B Umpire Rackley thus was in the best position of any person to observe the ball as it arrived at the planar edge of the Green Monster, meaning that MLB referred to his on-field ruling of "home run" for lack of evidence to indicate otherwise.
Related PostAsk UEFL - Judging a Fly Ball as Fair or Foul (Video) (7/13/18).

Video as follows:

Alternate Link: UEFL analysis and explanation regarding parallax angle & "call stands" (UEFL)
Second Video: Michael Chavis hits a solo home run in the 2nd that stands after review (BOS)


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