One of Major League Baseball's latest controversies calls to mind a bit from the 2009 Star Trek, in which Dr. McCoy offers words of wisdom to Mr. Spock.

"You know, back home we have a saying: 'If you're gonna ride in the Kentucky Derby, you don't leave your prize stallion in the stable.'"

This applied to Kris Bryant back in 2015, and to Ronald Acuna Jr. earlier in 2018. Right now, it applies to Vladimir Guerrero Jr., Eloy Jimenez and Peter Alonso.

The arrival of expanded rosters on Sept. 1 also marked the arrival of cup-of-coffee season for deserving players from the minor leagues. Because each one is a top-rated prospect who's put up huge numbers in the high minors, there's little doubt Guerrero, Jimenez and Alonso should be among the lucky coffee drinkers. If anything, they all deserved to be promoted a lot sooner than September.

Yet they are nowhere to be seen. Guerrero is not with the Toronto Blue Jays. Jimenez isn't with the Chicago White Sox. Nor is Alonso with the New York Mets.

Such is the effect of the menace known as "service-time manipulation."

For anyone who needs a quick primer, this is the practice that sees teams keep players in the minors until they have secured their services for an additional year.

A player can't reach free agency until he's played six seasons in the majors. But while an MLB season plays out over roughly 180 days, a player qualifies as having played in a "season" if he's in the majors for at least 172 days. Any less than that, and he falls short.

So if a team waits to bring along a top prospect until after the 172-day cutoff, it can control him for the remainder of that season plus six more afterward. In effect, that player has to wait seven years until free agency.

Hence Guerrero, Jimenez and Alonso probably won't be seen until the middle of April 2019, when the fateful cutoff will have come and gone.

As Sheryl Ring wrote for FanGraphs in March, there's a possible legal argument against service-time manipulation—that teams who engage in it aren't acting in good faith with regard to competitive aspirations.

Where things get complicated is that when prospects are ready for The Show is subjective. There isn't a set of boxes to check. Clubs are free to determine their readiness based on...well, whatever.

Back in '15, the Chicago Cubs asserted that Bryant needed to improve his defense. Earlier this year, the Atlanta Braves reasoned that a 20-year-old Acuna shouldn't be rushed to the majors.