Oh, what a difference 11 days can make.

Most baseball fans aren’t privy to the mysterious world of “service time.” And why should they be? We go to the ballpark to watch icons launch mammoth home runs, not to get lost in the intricacies of baseball’s labor agreement. Service time, however, is an exceptional little footnote to the rules of the game, and a fascinating monkey wrench thrown into a GM’s roster calculus. At best, understanding the rules of service time can give you an appreciation for the complexities of a GM’s decision-making process and teach you to be a better critic of your team’s management. At worst, it’s fodder for barroom trivia that will fill you with the dorkiest sense of pride as you educate your friends.

The implications of the rules aren’t trivial. A prime example comes from David Schoenfield of ESPN. On July 8, 1994, the Seattle Mariners called up an 18-year-old super prospect named Alex Rodriguez. He would play 17 meaningless games for a team that would finish well below .500, only to be sent down to the minors for the remainder of 1994 and the majority of 1995. Five years later, following the 2000 season, Rodriguez walked away from the M’s as a free agent, signing a megadeal with the division rival Texas Rangers. Why does any of this matter? Had the Mariner’s brass held off on their 17-game experiment, Rodriguez would have accrued one less year of service time, keeping him locked under team control until after the 2001 season. You know … the season where the Mariners won 116 games even without him.

The rules aren’t too tough to digest. Essentially, for every day that a player is on his team’s major league roster, he accrues one day of service time. The MLB season is approximately 182 days long, and if a player racks up 172 days on the roster he is credited with a full year of service time. Until a player has compiled six full years of service time, he is NOT eligible for free agency. That means that he is bound to his team, earning league minimum salaries for the first three years and arbitration-determined salaries for the next three years. Even arbitration salaries, however, fall well below what a player would receive as a free agent, making these six years an invaluable bargain for any team. There are a few other technicalities that prevent teams from manipulating the rules, but for the most part, this is the policy under which teams make decisions.

The incredible value of a superstar earning only league minimum or arbitration salaries can’t be overstated. Particularly for small-market teams that have no choice but to let their stars walk away during free agency, one extra year of “team control” can be worth tens of millions of dollars. Had A-Rod been under team control with the Mariners during the 2001 season, there’s no telling what that team might have accomplished.

This value is precisely why service time calculations are so important. Consider the following scenario. Yesterday (Tuesday), highly-touted Mariners starting prospect Michael Pineda made his major league debut. Assuming he stays on the Mariners’ roster for the remainder of the season (fairly likely considering some of the technicalities of the service time rules), he will accrue a full 182 days of service time, giving him a full year. This means that, barring a long-term reassignment to the minors, Pineda will be a free agent after the 2016 season.

What if, instead, the Mariners had kept Pineda in the minor leagues until April 11 — less than 2 weeks into the season? Pineda would be with the major league club for over 93 percent of the season, but he would only accrue 171 days of service time — one day below the cutoff for a year of service time. Further technicalities would prevent the Mariners from repeating the exercise each year, but the one missing year of service time would mean that Pineda wouldn’t become a free agent until after the 2017 season, saving the Mariners a year of his services and a boatload of money.

So why did the Mariners choose not to hold Pineda back? 11 extra days in the minors would have amounted to only two starts for a team that probably won’t make the playoffs anyway, so holding him back wouldn’t have made a difference for this year’s club. It certainly would be worth the full extra season of team control in 2017. But there are other costs associated with holding a player back. For one, you can bet that players know the rules just as well as GMs, and many consider it a slap in the face to have their service time “manipulated.” Some GMs figure it isn’t worth disturbing the player-team relationship. On top of this, holding talented prospects in the minors never sits well with the fan base. It’s also possible that most GMs plan to lock up talented prospects on long-term contracts and thus don’t care about the team-control pay scale (although this argument is baloney since one extra year of free agency gives players that much extra leverage in contract negotiations). Another potential explanation is that major league front offices don’t give these calculations sufficient thought.

Either way, the decision of whether to hold prospects back for an extra 11 days at the start of the season is more common than you would think. In 2008, Evan Longoria spent the first 13 days of the season in the minors before getting the call to the show (although that might have been due to an injury to Willy Aybar). Last year, the Braves faced the same dilemma with Jason Heyward and elected not to hold him back, while the Giants chose to save Buster Posey’s debut for May. This year, uber-prospects Jesus Montero (Yankees), Zach Britton (Orioles) and Mike Minor (Braves) all started the season in the minors. Were these decisions made solely on the basis of service time? No. But don’t believe your GM when he tells you that these weren’t an important consideration.

In the end, service time calculations don’t dictate how GMs behave, but it’s naïve to think that they’re not an important piece of the puzzle, particularly for small-market teams that rely on team-controlled prospects to round out their rosters. The next time your team waits until April 11 to debut the franchise’s coveted young talent, you’ll know why.

John Ettinger is a junior in Saybrook College.