For the second time in a handful of years, the biggest story in Major League Baseball concerns the ball itself. Unlike a few seasons back, when it appeared the league had (intentionally or not) juiced the ball in order to stimulate offense, this time the concern has to do with what substances are being applied to the ball by pitchers to generate more impressive movement.

Just last week, MLB signaled that the league intended to crack down on the use of foreign substances on the mound. Numerous pitchers have since posted lower-than-usual spin rates, leading to frenzied speculation about who is or has been doctoring the ball. Yankees ace Gerrit Cole, one of the accused, offered a less-than-convincing answer on Tuesday when he was asked whether or not he had ever used Spider Track, an adhesive designed for strength competitions. 

Because there are a lot of moving parts to this story, we here at CBS Sports decided to put together a primer answering some of the biggest questions the average fan might have about MLB's sticky situation. With that in mind, let's get to it.

1. What spurred this controversy? 

Technically, this has been years in the making. Once teams were able to quantify spin rates and other advanced pitch analysis metrics, it was a matter of time before they took to using substances to improve upon those marks. Dodgers right-hander Trevor Bauer publicly accused the Astros of loading the ball to improve their spin rates back in May of 2018. (Bauer has since seen his own spin rates increase, which is notable since he stated the only way to add spin was through the use of grip-enhancing substances.)

The league issued a memo to teams in the spring that umpires would be more aggressive in enforcing rules against the use of foreign substances. Nothing much came of that, however, and the league had to re-signal last week that it would crack down on offenders through random checks and spin-rate analysis.

2. Haven't pitchers always done this?

For a long, long time, yes. Baseball first passed legislation banning spitballs and other trick pitches back in 1920, according to Derek Zumsteg's invaluable Cheater's Guide to Baseball. That hasn't stopped moundsfolk from hiding and using various substances and instruments over the years, including (and not limited to) pine tar, sunscreen, emery boards, sandpaper and whatever else they can rub on their hats or gloves or hide away on the inside of their belt buckle. 

Pitchers are, in other words, resourceful and desperate little rascals who are willing to violate MLB rule 6.02(c)(7) -- the one that states pitchers may not have "on his person, or in his possession, any foreign substance."

Their past use of grip-enhancing substances was covered by the explanation that it made throwing a baseball a safer activity for the hitter. There was also some gamesmanship involved, as opposing managers didn't want to call attention to other team's pitchers violating the rules, lest their own pitchers be investigated and found to be committing the same sins.

3. Why does it matter now?

The league's hitters are on pace for their lowest batting average and highest strikeout rate in history. Hitting has become too difficult, with pitchers possessing more velocity and movement than their past counterparts. The league seems to believe part of the improvement in stuff has to do with the use of foreign substances, and that assertion likely has some merit.

The substances pitchers are using now appear to be better at enabling pitchers to spin the baseball. The Score's Travis Sawchik conducted an experiment in which the use of Spider Track allowed a pitcher to not only gain some 500 RPMs on their fastball when compared to the baseline, but to also gain 500 RPMs as compared to their spin rate when they used pine tar.

4. Which pitchers are using substances?

There's no saying for sure, but a former Angels clubhouse attendant who was known for supplying a homemade grip-enhancer to pitchers filed a lawsuit over the winter that named several high-profile players as customers. Among them: the aforementioned Cole, Justin Verlander, and Max Scherzer. Those three have combined for five Cy Young Awards.

5. Who has been investigated?

To date, Bauer is the only pitcher known to be investigated. Cardinals reliever Giovanny Gallegos did recently have his hat confiscated by umpire Joe West after it appeared to have foreign substances on the brim. Though Gallegos wasn't ejected or suspended, Cardinals manager Mike Shildt took exception with West's behavior after the game by saying, "This is baseball's dirty little secret, and this is the wrong time and the wrong arena to expose it."

Shildt continued: "You want to police some sunscreen and rosin? Go ahead. Get every single person in this league. ... Why don't you start with the guys that are cheating with some stuff that's really impacting the game?"

6. Has anyone been punished this year?

Yes, just not at the big-league level. Four minor-league pitchers have been ejected and then suspended 10 games apiece after umpires found foreign substances on their person: Marcus Evey (White Sox), Sal Biasi (White Sox), Kai-Wei Teng (Giants), and Mason Englert (Rangers).