The NFL's quarters rule is one that has been mired in controversy since its inception in 1990. It's back in the news after it kept Christian McCaffrey from reporting to the team's offseason program until Thursday, and he's not the only one that's been affected by the rule this year.

But what is the quarters rule exactly, and is it something that the league should consider revising? We break it down below.

What is it?

The premise of the rule is that draftees cannot report to training camps until their school's year is completed. It is designed to discourage students from dropping out of school and thus foster good graduation rates from schools' athletic programs.

Players that have final exams that end before May 15 are allowed to begin participating in official team activities on that day, whereas players that have exams after May 15 cannot participate until their exams are completed.

The rule applies to the six schools that employ the quarters system: Stanford, Washington, Northwestern, Oregon, Oregon State and UCLA.

Why does it matter now?

When the rule was applied to Panthers running back and Stanford student Christian McCaffrey this week, his new teammates had words for the NFL.

Tight end Greg Olsen said that "At the end of the day, these kids are being hurt. Here's a young kid looking to come in and become acclimated with a new team and join the NFL and make a huge step in his life. Because of something completely out of his control, he's forbidden from being with us."

Olsen also implied that the deal may have been a quid pro quo situation between the NFL and the NCAA.

Although players dislike the rule, NFL VP of football operations Troy Vincent stands by it.

"If dropouts were allowed to report to their clubs early, the student-athletes who remain in school would be put in a competitive disadvantage. ... They could face pressure from clubs and their fans to participate in offseason activities," he said.

Could the rule be changed? 

The debate lies in where the competitive disadvantages are and how disadvantageous it can be for a later-round draft pick to miss any time. However, the NFL has stressed the importance of graduation rates and how players dropping out for camps can negatively affect the game at both levels.

"Graduation rates were very important to colleges then, as they are now," the NFL elaborated in the link that Vincent tweeted. "When drafted players dropped out without graduating, it created an issue for the colleges. The American Football Coaches Association -- an association of football coaches and staff on all levels -- reacted by locking pro scouts off of college campuses."

It's a debate that has gone on for some time, and as players continue to get more vocal about it the NFL may have to at least consider revisiting it. As it stands, however, the NFL appears to have no intention of changing the rule, and they believe that the benefits of the rule outweigh the perceived negative repercussions.