SEA Replay - Cubby's Pitching Motion Rules Check

In the wake of MLB's Carter Capps delivery rule, Chief Fieldin Culbreth's crew initiated a Replay Review Monday in Seattle regarding Mariners relief pitcher Cory Gearrin's motion in the 7th inning, supporting HP Umpire DJ Reyburn's initial assertion of an illegal pitching move as a result of a double-step during Gearrin's motion home.

What was the rule being discussed and was Reyburn's instinct correct?

Gearrin's Illegal Move: During warmups after entering Monday's A's-Mariners game, the right-handed Gearrin demonstrated his usual pitching motion: With his right foot (pivot foot) in contact with the pitcher's plate, Gearrin raised his left leg (free foot) before returning his free foot to the ground, slightly lifting this foot and moving it forward before planting further down the mound, and finally releasing the ball toward home plate.

The second step toward home is illegal.

Rule & Analysis: This is an illegal motion because of Official Baseball Rule 5.07(a) Comment's provision that "The pitcher may not take a second step toward home plate with either foot or otherwise reset his pivot foot in his delivery of the pitch. If there is a runner, or runners, on base it is a balk under Rule 6.02(a); if the bases are unoccupied it is an illegal pitch under Rule 6.02(b)." This rule applies for all pitching deliveries, regardless of whether the pitcher has opted to use Windup Position or to use Set Position.

The rule outlawing a second step toward home plate was added prior to the 2017 season in response to former big league pitcher Carter Capps' unique crow-hop delivery in which he reset his pivot in delivery of the pitch.
Related Post: Carter Capps Throws Illegal Pitch, Ejected After Hitting Ump (6/26/17).

Scott Servais disputes the crew's call.

For what it's worth, 6.02(a) simply states that such an illegal pitch is a balk with runners on base, while 6.02(b) states that the penalty for an illegal pitch with the bases unoccupied shall be a ball added to the count.

Preventative Officiating: Thus, Reyburn's instinct was correct—Gearrin's two-step maneuver is illegal and is more severe than a simple "don't do that" instruction; had Gearrin double-tapped his free foot during gameplay, it would have been an illegal pitch.

DJ Reyburn signals for a Replay Review.

Replay Review: After Reyburn informed Gearrin that his motion was illegal, protestation from Seattle brought the umpiring crew of Reyburn, Culbreth, Paul Nauert, and CB Bucknor together, which, after discussion with Mariners Manager Scott Servais, opted to initiate a Crew Chief Review for a rules check relative to OBR 5.07(a) and 6.02(b).

Six minutes? I'm with Dee Gordon (at 3:29).

After a two-and-a-half minute review, New York returned a verdict that confirmed Reyburn's suspicion, and Gearrin subsequently altered his pitching motion such that his free foot remained off the ground until reaching its final landing place, thus satisfying Rule 5.07(a) Comment's requirement that the pitcher not "take a second step toward home plate with either foot."

Total Delay & Pace of Play: The entire process took about six minutes from Reyburn's initial conversation with Gearrin until the resumption of play.

The game then proceeded and concluded without further incident (until Reyburn ejected Athletics Manager Bob Melvin an inning later following a ball four call and game-tying home run).
Related Post: MLB Ejection 054 - DJ Reyburn (1; Bob Melvin) (5/13/19).

Video as follows:

Alternate Link: Reyburn identifies an illegal pitch and addresses the issue prior to play (SEA)