As strikeout and walk rates drop, MLB umpires prepare to begin checking pitchers for foreign substances Monday, sources say

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Gerrit Cole vents about MLB's crackdown of foreign substances (0:34)

Gerrit Cole voices his frustration with issues gripping the baseball after MLB's attempt to regulate foreign substances. (0:34)

Beginning Monday, major league umpires will check pitchers for foreign substances after they've pitched -- with the exception of the closer, who will be inspected before entering the game -- sources familiar with the process said.

Pitchers will be inspected between innings and/or after they come out of the game unless they're exhibiting suspicious behavior during an inning. In that case, umpires have the right to inspect a pitcher between batters -- but not during an at-bat.

Initially, umpires will check the glove, hat and belt of pitchers, but if they suspect a reason to look elsewhere, they'll have the right to inspect other parts of a player's uniform.

Closers will be inspected before they pitch in order to avoid awkward confrontations with umpires in case they blow a save and the game ends in a walk off.

If a pitcher is found to have a foreign substance on him he'll be ejected from the game and suspended 10 days. Umpires were informed of the details in a conference call on Saturday.

The threat of the upcoming crackdown might have already had an impact on the game as pitchers do away with their foreign substances.

The month of June has seen the lowest strikeout and walk rates, while producing the highest batting average, on-base percentage and OPS of any month so far. It remains to be seen if that's crackdown-related or includes hitting in warmer weather.