Enforcing a rule that is in the rulebooks might seem obvious. But for the most part, there has been a tacit understanding that Major League Baseball¡¯s rules prohibiting the use of foreign substances by pitchers had some wiggle room. Managers, players and teams generally agreed that as long as hurlers were not making a mockery of the rulebook (and the opposition), a little ¡°sticky stuff¡± was no big deal.

This dynamic is changing here in 2021.

Following guidance from the Commissioner¡¯s Office that was put into effect June 21, Rules 3.01 and 6.02(c) and (d) will be enforced by umpires, and pitchers caught with foreign substances will face suspension. Clubs will not be able to fill the roster spot while a player is under suspension.

¡°After an extensive process of repeated warnings without effect, gathering information from current and former players and others across the sport, two months of comprehensive data collection, listening to our fans and thoughtful deliberation, I have determined that new enforcement of foreign substances is needed to level the playing field,¡± Commissioner Robert D. Manfred, Jr. said in a statement announcing the changes. ¡°I understand there¡¯s a history of foreign substances being used on the ball, but what we are seeing today is objectively far different, with much tackier substances being used more frequently than ever before.¡±

Here¡¯s an FAQ on how we got here and what it means.

What do the rules say?

Rule 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.¡±

The rule gives the umpire the power to remove any offenders from the game immediately and for the league to impose a 10-game suspension under Rule 3.01 and past precedent. The standard appeals process will be in place for foreign substance-related discipline and players will be paid during these suspensions.

Rule 6.02 expands on 3.01 by stating, among other things, that a pitcher may not ¡°apply a foreign substance of any kind to the ball;¡± ¡°deface the ball in any manner;¡± "throw a shine ball, spit ball, mud ball, or emery ball;" ¡°have on his person, or in his possession, any foreign substance;¡± or ¡°attach anything to his hand, any finger or either wrist (e.g., Band-Aid, tape, Super Glue, bracelet, etc.).¡±

Why are they being more strictly enforced now?

As pitchers have learned via ball tracking data the true effect of spin rates on performance, they have increasingly turned to foreign substances to improve their spin. The effect on offensive performance has become pronounced. Through the first two months of the 2021 season, the league batting average (.236) was on pace to be the lowest in history -- one point lower than the 1968 league average that prompted a change to the height of the mound.

MLB had informed clubs prior to the 2021 season that it would be making an effort to quantify the prevalence and effects of foreign substances in the sport through the use of data collection, on-site monitoring of the clubhouse and dugout areas, video review and the collection of balls taken out of play. This process, along with complaints from position players, pitchers, umpires, coaches and executives, spurred the new guidelines, which were announced on June 15 and go into effect on June 21.

¡°It has become clear that the use of foreign substance has generally morphed from trying to get a better grip on the ball into something else -- an unfair competitive advantage that is creating a lack of action and an uneven playing field,¡± Commissioner Manfred said. ¡°This is not about any individual player or Club, or placing blame, it is about a collective shift that has changed the game and needs to be addressed. We have a responsibility to our fans and the generational talent competing on the field to eliminate these substances and improve the game.¡±

Previously, the enforcement of the rule was mostly left up to managers, who could ask the umpire anytime to check the opposing pitchers for a violation. This became less common over the years, presumably because managers feared that if they checked the other team, other teams were more likely to come after their hurlers. Under the new guidelines, umpires will enforce the rule whether asked by a manager or not.

What are the new guidelines?

They are as follows:

? Starting pitchers will have more than one mandatory check per game, and each relief pitcher must be checked either at the conclusion of the inning in which he entered the game or when he is removed from the game (whichever occurs first). In general, inspections will be conducted between innings or after pitching changes to avoid a delay of the game and to allow the umpire to perform a thorough check, including the hat, glove and fingertips of the pitcher.

? Umpires may perform a check at any time during the game when the umpire notices the baseball has an unusually sticky feel to it, or when the umpire observes a pitcher going to his glove, hat, belt or any other part of his uniform or body to retrieve or apply what may be a foreign substance.

? A player who possesses or applies foreign substances in violation of the rules will be immediately ejected from the game and suspended (with pay) for 10 games. The umpiring crew shall be the sole judge as to whether the rules have been violated. The use of foreign substances is not subject to challenge using the replay review system.

? Although the foreign substance prohibitions do not apply exclusively to pitchers, the pitcher ultimately will be responsible for any ball that is delivered with a foreign substance on it. If a player other than the pitcher is found to have applied a foreign substance to the baseball (e.g., the catcher applies a foreign substance to the baseball before throwing it back to the pitcher), both the position player and pitcher will be ejected and automatically suspended.

? Catchers will also be subject to routine inspections. Umpires will also inspect a position player if they observe conduct consistent with the use of a foreign substance by the pitcher. Position players will not be ejected for having a foreign substance on their glove or uniform unless the umpire determines that the player was applying the substance to the ball in order to aid the pitcher.

? A player who refuses to cooperate with an inspection conducted by the umpire will be presumed to have violated the rules, resulting in an ejection from the game and a suspension.

? Rosin bags on the mound may be used in accordance with the rules. All substances except for rosin are prohibited per the Playing Rules that clearly state players cannot ¡°apply a foreign substance of any kind to the ball¡± and may not ¡°have on his person, or in his possession, any foreign substance.¡± Players may not intentionally combine rosin with other substances (e.g., sunscreen) to create additional tackiness or they risk ejection and suspension. Pitchers have been advised not to apply sunscreen during night games after the sun has gone down or when playing in stadiums with closed roofs. To ensure standardization of the rosin bag, Clubs must submit the rosin bag along with the game balls to be reviewed by the umpires before the start of each game.

? Club personnel who help players to use foreign substances, handle foreign substances, mask player use of foreign substances, interfere with collections of baseballs or otherwise fail to report such violations of the playing rules will be subject to fines and/or suspension by the Commissioner.

? Any club employee who encourages a player to use foreign substances, or otherwise trains a player how to utilize a foreign substance in violation of the rules, will be subject to severe discipline by the Commissioner up to and including placement on the Ineligible List.

? Clubs and club personnel are subject to sanctions for failing to adequately educate and manage or police their staff and players to ensure compliance with the rules. The Department of Investigations will investigate clubs whose players repeatedly violate the rules to determine the extent to which Club personnel were aware of or otherwise condoned the practice.

? Clubs may not replace on the roster a player who is suspended for any on-field violation.

? MLB will closely monitor the effect of this policy on competition, and on player health, and may make future modifications to the enhanced enforcement guidance as appropriate.

How will this affect hit-by-pitch rates?

Concern about rampant hit-by-pitches has long been cited as a valid excuse for pitchers to use foreign substances to improve their control and promote batter safety. And yet the hit-by-pitch rate through May 31 of this season (prior to pitchers beginning to reduce their use of foreign substances in anticipation of the new guidelines) was the highest of any season in the last 100 years. And the previous three seasons were the next three highest on record.

So while we don¡¯t yet know what impact these changes will have over the long-term, we can say that the situation was not great to begin with, and hit-by-pitches has remained flat over the last three weeks while spin rates have dropped across the league.

What are some other indicators to be mindful of?

While spin rate can tell you a lot, spin-to-velocity ratio is perhaps the best metric to analyze year-to-year trends since it normalizes for increases in velocity. At a league-wide level, that number has been dropping since in the weeks leading up to the new enforcement rules. In fact, the week prior to June 21 saw an overall spin-to-velo ratio of 23.9, which is roughly in line with what we saw during the 2015 season. Meanwhile, we saw the lowest strikeout rate (22.5%) and the lowest walk rate (8.2%) of any week of the season.

Additionally, offense is up across the league, as June has highest batting average of any month of the season.

Has anything like this enforcement ever happened before?

Pitchers have applied foreign substances to the baseball almost as long as there has been a baseball. The first rules prohibiting players from discoloring or otherwise damaging the ball date back to the late 1800s. But early in MLB¡¯s modern era, which dates back to 1901, the success of pitchers like Jack Chesbro and Ed Walsh led to the popularization of the spitball. Pitchers spat on and scuffed the ball with little concern of enforcement, as the only penalty was a $5 fine.

That changed in 1920, the first year the spitball and other defaced balls were more formally banned with the implementation of the 10-game suspension. But because the spitball had gained such prominence in the years leading up to that decision, 17 pitchers identified as spitballers were permitted to continue to throw that particular pitch (though they could not otherwise deface the ball). The last of these grandfathered pitchers was Burleigh Grimes, whose retirement in 1934 marked the end of the legal spitball and essentially left us with the rules we have on the books today. However, what we are seeing now, in prevalence, and the types of substances (such as Spider Tack) being used to gain a competitive advantage, is different and unprecedented.

Have those rules always been flouted?

In a word, yes. Enforcing the spitball rules proved difficult, and the pitch regained popularity in the middle of the 20th century. Ford Frick, who served as Commissioner from 1951 to 1965, even pushed -- unsuccessfully -- for the legalization of the pitch.

The spitball was finally more successfully outlawed in 1967, when MLB adopted the section of Rule 6.02 that prohibits the pitcher from touching the ball after touching his mouth or lips and requiring him to wipe the fingers of his pitching hand dry. This compelled pitchers to use foreign substances -- such as Vaseline, pine tar and, eventually, sunscreen and rosin -- with greater regularity.

The 1967 rule adjustment compelled managers to more forcefully request that umpires inspect opposing pitchers for such substances, but that ultimately didn¡¯t last. Hall of Famer Gaylord Perry so notoriously ran afoul of the rules that his autobiography is titled, ¡°Me and the Spitter.¡± Joe Niekro famously and hilariously tried to quickly get rid of a piece of sandpaper and an emery board when an umpire went to check him in 1987, but he otherwise went mostly unchecked. And in recent years, as foreign substances have become even more rampantly used thanks to a greater understanding of their effects on spin rates, the manager requests became exceedingly rare. Actual enforcement, such as when Yankees pitcher Michael Pineda was suspended 10 games for the use of pine tar in 2014, was very much more exception than rule.

Has MLB made other recent efforts to address this issue?

Yes. MLB has spent several years working with Rawlings and others on the development of prototypes and various forms of testing for a new, tackier baseball that is easier for pitchers to grip without the use of foreign substances.

In 2019, MLB showcased a prototype for one day in each Spring Training camp. Pitchers threw bullpens with them to provide their feedback (the balls were not used in Spring Training games).

The prototypes have been examined by general managers. experimented with as part of MLB¡¯s partnership with the Atlantic League and were used in several Arizona Fall League games in 2016. Though the coefficient of restitution (COR) of the different ball has been comparable to the regular ball, much more in-game testing will be needed to determine the drag factors.

The above has been a learning exercise, but the ball has not yet proven to be a viable alternative for use in the Major Leagues.

Isn¡¯t mud applied to the baseballs?

Yes. Lena Blackburne Baseball Rubbing Mud is used by every team in both the Major and Minor Leagues. MLB's official rule book says that each ball must be ¡°properly rubbed so that the gloss is removed.¡±

In 2020, MLB implemented a set of standards for each club to follow in how they apply mud to baseballs before the game.

Is there precedent for a midseason rules change?

The implementation of instant replay is the most notable precedent. Replay itself was instituted on home run and fair-or-foul calls in late August 2008. And several weeks into the 2014 season -- the first year of expanded replay -- MLB clarified the meaning of ¡°possession¡± of the ball for infielders turning double plays on force outs. Fielders no longer had to successfully remove the ball from their glove with their throwing hand in order for it to be ruled a catch.

In other sports, we¡¯ve seen the NBA revert from a synthetic basketball to the traditional leather ball midseason in 2006-07 after players suffered a rash of hand injuries. In Super Bowl LII in 2018, there was much public scrutiny over whether a new catch rule that wound up going into effect the following season was implemented early, though the NFL denied it.