Block in the back
 

Are these fouls always enforced from spot of foul and never from the LOS? Had a 60 yd run but foul called 10 yds beyond LOS. Ball was on 15 yd line.

Not sure about NCAA but in NFHS, a block in the back is enforced under the all but one principle. Fouls that fall under this principle are all enforced from the basic spot (for a running play this is the end of the run) except for fouls by the offense behind the basic spot (this is the "but one").

So for your play, if the run ended at the defense's 35 yard line, but the offense commited the foul at their 25, it would be enforced from their 25 since the spot of the foul is behind the end of the run (basic spot).

Does that make sense?

Also, it's an "illegal block in the back." There are legal blocks in the back, after all.

A's ball on their 40 yard line. A12 drops back to pass and is clearly out of the free blocking zone. After the pass is released A50 blocks B90 in the back. The block occurred in the expanded neutral zone, at A's 41 yard line.

This is a loose ball play. The basic spot is the previous spot. The foul occurred beyond the basic spot. Under all-but-one the foul in enforced from the basic spot.