Going into studying the rules with zys we're finding a whole bunch more doubts on the book... for starters

Rule 2-7-1-c states:
c. A valid or invalid fair catch signal deprives the receiving team of the
opportunity to advance the ball, and the ball is declared dead at the spot
of the catch or recovery or at the spot of the signal if the catch precedes
the signal (Rule 6-5-1-a Exception).

What does "or at the spot of the signal if the catch precedes
the signal" means?

It means: wherever the player was when he signaled, on condition that the catch happened before the signal.

Play example, Team A punts, Team B's punt returner catches the kick and starts running. Either because he hopes to confuse the kick coverage team or because he is a 16 year old kid, he gives a fair catch signal as he is running. Officials should get on the whistles and shut things down as ball was dead as soon as the signal was given. The catch was before the signal but the signal causes ball to become dead.

In this case, are there any penalties?

Under NCAA rules, there is no penalty other than ball becoming dead at the spot it was when the signal was given. If the returner gives the signal and continues to advance, then you could enforce the dead ball delay penalty but I would not do that unless the covering officials had noticed what transpired and tried to shut things down but the returner kept running

A doubt about fumble in the end of a half
 

In the NFL, if a fumble occurs in the last two minutes of a half, only the player that suffered the fumble may recover and advance it. Is it the same in the NCAA?

On 4th down only in the NCAA and also on 4th down in the NFL.

In the NCAA this rule applies on all 4th downs and all try downs, regardless of time remaining. (Should be noted that once there has been a change of team possession during the down, this rule no longer applies, i.e. Team A fumbles, Team B (#B24) recovers, and then B24 fumbles. Anyone from either team can recover and advance the fumble. And should A recover it but fumble again, anyone can advance and recover)

Another one...
 

A.R. 7-3-8-XIX states:

On a legal forward pass beyond the neutral zone, A80 and B60 are attempting to catch the pass thrown to A80’s position. A14, who is not attempting to catch the pass, blocks B65 downfield, either before the pass is thrown or while the uncatchable pass is in flight. RULING: Team A foul, offensive pass interference. Penalty—15 yards from the previous spot.

Why is this a foul if the pass was not catchable by B65 or hadn´t been thrown?

Philosophically, that is a very good question. This ruling highlights a key concept with regard to pass interference, the offense is much more restricted than is the defense. The rulemakers have decided that the offense should be more restricted in order to keep the game "in balance". Therefore, Team A cannot do some things that Team B is permitted to do.

Bottom line, the written rules prohibit (starting at the snap) the contact downfield by the offense on a play like this. Furthermore, the catchable/uncatchable component only applies to Team A contact when the contact is near where the ball is thrown. I believe the feeling is that by blocking away from the pass, the offense "tricks" the defense unfairly as the defender assumes this will be a running play since he is being blocked downfield.

Rule 9-3-4-g states:

A defensive player may not continuously contact an opponent’s helmet (including the face mask) with hand(s) or arm(s) (Exception: Against the runner).

So is it legal against the runner? It seems wrong.

They wanted to keep the rule fairly simple, so blocking downfield by A is prohibited until the pass is thrown beyond the neutral zone, if a pass is then thrown beyond the neutral zone. Another way of putting it is that it's illegal to throw a pass beyond the neutral zone if during that down a player of A has already blocked beyond the neutral zone -- but they didn't write it that way because they wanted the foul to be by the blocker rather than its being an illegal pass. There are certain advantages of compactness of language by making this part of the provisions on pass interference rather than the legality of the pass.

This might be one of the things you might consider changing for your country once you have the translation completed. Maybe it would be simpler to consider the pass to be the violation in that case, and to penalize it by making it incomplete. But you must consider now that there's no loss of down with the offensive pass interference, the loss of down incurred by making it an illegal forward pass might be a more severe penalty in some cases than the distance with down repeated.

Robert in the Bronx

No, that isnt a possibility. Brazil has joined IFAF so that they can become part of World American football and join the 50 or so other countries worldwide. IFAF play straight NCAA Rules so Brazil need to do the same.


OPI
TXMike hit the nail on the head about OPI, when he talked about the defense expecting a run when they are blocked by the offense.

In a similar way to how we as officials read a play by the blocking, then the defensive secondary read a play by whether the receivers run pass routes or whether they come out and run block.

The action of the defensive secondary when they see a teammate be blocked or they are blocked is to try and lose the offensive guy and find the runner and make the tackle.

If the pass is not thrown, then there is no OPI foul. There must be a forward pass occur for OPI.

If the pass is caught behind the NZ, then there is no OPI foul. Only if there is a forward pass that crosses the NZ can there be OPI.


Yes it is legal. It is regarded as part of attempting to make the tackle.

There are of course variations on the rules in a lot of the countries that also play IFAF. Generally though they are very small changes, or limited to administration issues (but not always).
One that always bugged me, but the Germans won't change is that they took out rule 1.4.11 Use of Tobacco.

Rules are about equal advantage. In this case A14 is restricted from blocking because he knows or should know a pass play is in progress (NFHS 7-5-7 - 15 yards and loss of down).

A B player who does not know the play is restricted from interference with receiving a pass until when the pass is in the air on theory B has to guess until the pass is thrown whether the play is a pass play.

However, during the late 80s defensive backs gained an advantage when they began "chucking" offensive receivers -- blocking them off their routes by basically giving them a shove. NCAA and NFHS (9-2-3d) made this illegal use of hands to keep the rules in balance as chucking had given the defense an unfair advantage.