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Major League Baseball intends to increase enforcement of the league's foreign substance policy in 2023. On Thursday, MLB vice president Michael Hill issued a memo to all 30 clubs informing them umpires have been encouraged to ramp up foreign-substance checks this season, reports The Athletic. Foreign-substance checks were implemented on June 21, 2021.

Here are the details on MLB's heightened foreign substance checks:

  • Umpires' inspections of pitchers' hands and fingers, which began last season, would be more thorough than the often-perfunctory inspections that umpires performed last year.
  • Those inspections would also be more random, as opposed to last season, when inspections of starting pitchers were generally performed after the same innings every game.
  • Umpires also could resume checking pitchers' caps, gloves and belts — a practice they employed in 2021 but abandoned in 2022 in favor of more streamlined inspections of hands and fingers.
  • Most significantly, umpires would be empowered to be more aggressive about inspecting pitchers than in the past. 

Last season 871 players threw a pitch in a major-league game and not one was caught with a foreign substance. It would be naive to think that means foreign substances are out of the game entirely. It means enforcement is lacking, so MLB is ramping it back up.

Once upon a time pitchers used foreign substances to doctor the ball and get unnatural movement, or simply get a better grip to improve their control. In recent years pitchers have weaponized foreign substances, or "sticky stuff," to generate extreme spin rates and movement. That has contributed to the increase in strikeouts throughout the game.

Here is the league average four-seam fastball spin rate the last two seasons:

  • Opening Day 2021 to June 20, 2021: 2,308 rpm (no foreign substance enforcement)
  • June 21, 2021 to end of 2021 regular season: 2,248 rpm (foreign substance checks begin June 21, 2021)
  • Opening Day 2022 to 2022 All-Star break: 2,264 rpm
  • 2022 All-Star break to end of 2022 regular season: 2,292 rpm

For an individual pitcher, a change of 50-60 rpm of spin rate is nothing. That fits within normal game-to-game fluctuation, similar to a pitcher sitting 94 mph one game and 95 mph the next. Spin rate changes in the 200 rpm range hint at sticky stuff use.

For an entire league though, a 50-60 rpm change suggests foreign substances were widespread. The league average fastball spin rate declined significantly after sticky stuff checks were implemented in June 2021, but it has since gradually climbed back up, and by the end of 2022 it was almost where it were before the checks. That indicates pitchers are better at hiding sticky stuff or are using a substance that is more difficult to detect, or both.

Only two players -- lefties Héctor Santiago and Caleb Smith in 2021 -- have been suspended for foreign substances since the checks began. First-timers are hit with a 10-game suspension and repeat offenders can be penalized more heavily.