Schools can sign only 25 recruits in a class (initial counters). In simple terms, a grayshirt delays his enrollment to the next year while a blueshirt walks on, gains a scholie at some point, can play immediately but is counted against the next recruiting class numbers. Of course, this is the NCAA, so there’s nothing simple about it.
Technically, there are no more grayshirts since the rules were changed a few years ago eliminating oversigning – today a grayshirt doesn’t sign a Letter of Intent, so there’s nothing binding between the school and player. But prospects delaying enrollment are still referred to as grayshirts in the greater media so we’ll call them grayshirts here.
Grayshirts today essentially have a verbal agreement with a school that his scholie will be available next class and he’ll arrive to school the following January (or in the summer). The prospect will usually sign some type of “letter” from the school on Signing Day, but it has nothing to do with the NCAA. It can promise he’ll be placed on scholie next year, but there’s nothing enforceable about the letter. It’s basically a way to give a prospect something to sign with family and friends in a high school auditorium on Signing Day.
A prospect sometimes grayshirts when he hasn’t met NCAA qualification standards – but not always. There can be other reasons; the current numbers on the roster or in a recruiting class at a particular position, or a school wanting a player to mature physically another year before joining the program being a couple of them.
Meanwhile, blueshirting is gaining popularity. The NCAA allows athletes who were "not recruited" to arrive on campus as walk ons, accept scholarships during fall camp or at a later point in time, be eligible to play that same season and still be counted against the next recruiting class.
For blueshirts, who can arrive to a school as early as May, they have to pay their own way until they are put on scholie. Most schools promise that will be in fall camp, but there's nothing enforceable about when the school says the date is.
The NCAA defines a player as having been “not recruited” by a school as long as he 1) has not taken an official visit to campus, 2) had an in-home visit from the coaching staff or 3) does not sign an NLI or any kind of financial aid agreement with that school.
Blueshirting allows for a school to effectively take more than 25 initial counters – so long as they don’t go over the 85 scholarship limit. (Blueshirting is one hell of a loophole. That the NCAA did away with oversigning but still allows blueshirting is another in a long list of reasons to gaze upon the NCAA in wonder and amazement).
Cougar fans got a taste of blueshirting this past signing class when wide receiver Deontay Burnett, a longtime verbal commitment to WSU, decommitted at the last moment to blueshirt at USC. Burnett played as a true freshman this season for Southern Cal, appearing in 11 games and catching nine passes.
Blueshirting doesn’t always work out as planned. Three-star WR Jocquez Bruce out of Knoxville verballed to Tennessee in the summer before his senior year, and had a big signing day press conference the following February. But he did not sign a Letter of Intent at that ceremony, instead entering Tennessee in May as a blueshirt. In July, he left the program (without ever being put on scholie at Tennessee) in what was described as a mutual decision between Bruce and the UT coaching staff. He redshirted this past season at Middle Tennessee State (Conference USA).