Got a minute?
The differences seem to never end between NCAA and other rule sets. So let's talk about this item, that is also under discussion in another forum, because those working both sets, or who may want to move into NCAA football, will understand this correctly for NCAA.
Firstly, let's understand that a player is either inbounds or out of bounds. There is no "in between," even for an airborne player. To put it simply, while airborne, a player is where he was when he left the ground, even if his entire body is on one side or the other of a boundary line while airborne.
Secondly, all it takes is the slightest contact with a boundary line to make a player out of bounds, whether that contact is forced, intentional, or accidental. A player may re-establish himself inbounds, but that requires him to be in contact with the ground inbounds, with no part of his body touching anything out of bounds.
I have heard people say that if he just barely touches a boundary line, especially if very briefly, they will not consider him as having gone OB. THAT IS A HUGE DISSERVICE TO THE GAME, and such rulings won't stand the light of video review at the NCAA level. The playing field is 160' wide, and 360' long. Not 160'-1/8" wide. Not 360'-1/4" long. The players are expected to play within those boundaries (at ground level). The white lines are out of bounds. Period. End of story. To allow even the slightest violation to go un-called cheats the opponent out of their rule given expectation that both teams must play within those boundaries.
A player who is out of bounds is ineligible to touch a legal forward pass, even if he returns inbounds, UNLESS he was blocked out of bounds and returns inbounds "immediately."
A player who is blocked out of bounds (and even the slightest amount of contact with an opponent counts as a 'block,' for this rule) may restore his eligibility by re-establishing himself inbounds 'immediately,' which really means as soon as he is physically able. He may have to get to his feet after having been knocked down, or catch his balance, etc. But, as soon as he is able, he must return inbounds, or he loses his status as an eligible receiver, even if he does, thereafter, return inbounds.
A player who is out of bounds does not commit any foul by touching a player who is inbounds, or by touching the ball (loose, or in player possession). However, if he touches a live loose ball, the ball becomes dead, by virtue of the fact that it has touched something out of bounds. If a player who is out of bounds touches, or is touched by, a ball carrier, the ball remains alive.
An example is when a Team B player who is out of bounds consciously reaches back inbounds and touches a legally kicked ball during a free kick down. If that ball was previously untouched by Team B, then his touching constitutes an illegal kick out of bounds by Team A (like it or not). He does not commit any sort of foul for touching the ball.
During legal kick downs (free kicks or scrimmage kicks that cross the neutral zone), a Team A player that goes out of bounds commits a foul for an "illegal return" if he returns inbounds during the kick play portion of the down, UNLESS he was blocked out of bounds (with the exact same criteria for returning inbounds legally as discussed above). However, if he does return inbounds (other than after having been blocked OB and returning inbounds immediately), the only foul he commits is for returning inbounds. Once he returns inbounds, legally or illegally, he is not restricted as to what he may do, such as touching the ball, blocking an opponent, tackling a ball carrier etc., any more than any other player. He is still bound by rules governing illegal touching of the ball, and by blocking rules, etc., just like all of his teammates.
As an example, during a legal kick down, A88 runs out of bounds through his own team area, avoiding contact with an opponent, then returns inbounds and tackles kick receiver B22 after a very short return of the ball. The tackle is 100% legal. However, A88 returned inbounds illegally, so that foul can either cause a repeat of the down after a 5-yard penalty at the previous spot, or it may be added the spot where the dead-ball belongs to Team B.
Mechanically, ANY time we see an eligible receiver of Team A go out of bounds during a scrimmage down, or any player of Team A go out of bounds during a free kick or scrimmage kick play (remember the difference between a 'play' and a 'down'), the covering official is to drop his/her hat. The spot where the player goes OB is unimportant, so, just get your hat down in a way that everyone sees it, and it will present itself on video. That tells the whole world that we saw the player out of bounds. So, if we have to rule "Illegal Touching" of a legal forward pass by such a player, we at least have video evidence of the fact that we observed the player OB, with our hat as proof. Or, if we rule a legal touch/catch by such a player, because he was blocked out and returned immediately, we have video proof with the hat down.
Finally, in NCAA football, there is no such thing as "illegal participation." (Yes, there was, many years ago. But that went away a long time ago. No such thing in NCAA football.) So, take that out of your vocabulary.
There's probably more, but that's enough for now.
