Why Did Umps Allow Glasnow to Pitch Despite Sticky Hands?

During Cincinnati's 7-2 victory over LA on Thursday, umpire Bill Miller's crew found Dodgers pitcher Tyler Glasnow's throwing hand particularly sticky and discolored during a 2nd inning illegal substances inspection, but did not eject Los Angeles' starter for violation of the foreign substance rule. Given Laz Diaz's recent ejection of Astros pitcher Ronel Blanco for such a violation, why did Miller's crew allow Glasgow to remain in the game?

In June 2021, MLB issued new foreign substance guidelines designed to more strictly enforce Official Baseball Rules 3.01 and 6.02(c), both of which pertain to foreign substances.

OBR 3.01 states, "No player shall intentionally discolor or damage the ball by rubbing it with soil, rosin, paraffin, licorice, sand-paper, emery-paper or other foreign substance" while OBR 6.02(c) prohibits the following actions: "rub the ball on their glove, person or clothing...apply a foreign substance of any kind to the ball...deface the ball in any manner...have on their person or in their possession any foreign substance."

That last clause of OBR 6.02(c) is the most important because it prohibits a pitcher from simply possessing any foreign substance. It was this violation of OBR 6.02(c)(7) that prompted Diaz to eject Blanco two days before this Reds-Dodgers game. So why didn't Glasnow get the boot, too?

It all boils down to the type of illegal substance inspection conducted by the crew.

In Diaz's case, 1B Umpire Erich Bacchus detected something bizarre during an entry inspection in the 4th inning, or one conducted as Blanco took the field to pitch the top of the 4th. By contrast, Miller inspected Glasnow during an exit inspection after the Dodgers pitcher retired Cincinnati to end the top of the 2nd inning in LA.

The difference here is succinctly entry vs exit inspections, and, specifically, the rosin bag rule.

OBR 4.01(f) states "that an official rosin bag is placed on the ground behind the pitcher’s plate prior to the start of each game." Rosin is a legal substance and if an umpire detects rosin on the pitcher's hand, this is not grounds for ejection. However, the pitcher should only have rosin on their hand when actually pitching or directly after doing so, as the official, MLB-approved rosin bag is located on the field, not in the dugout and not in the bullpen.

Therefore, during an exit inspection conducted after a pitcher has been on the on-field mound and used the on-field rosin bag, it is not unusual for rosin to be on said pitcher's hand. If there is a question as to stickiness, the pitcher has plausible deniability (the "it's just rosin and sweat" line), and umpires who are suspicious but cannot prove anything can simply ask the pitcher to wash the hand prior to returning to the field the next inning.

But during an entry inspection, the pitcher from the dugout should not have any substance, including rosin, on their hand. The MLB-approved rosin bag is on the field, not in the dugout, after all.

And this is why most illegal substance ejections occur during entry inspections, rather than exit inspections: the rosin angle of plausible deniability cannot be used during an entry inspection, but can during an exit one.

Video as follows:
Alternate Link: Umpires allow sticky Glasnow to remain in game: about entry vs exit inspections