The difference is in not presuming a tackle would've occurred behind or at that spot due to the missed block, because the runner may have adjusted if he saw the situation develop.

However, the last NAGWS flag football rules I saw penalized 5 yds. & LD for blocking. So not all codes look at similar violations the same way.

A 10 or 15-yard penalty against the offense is often a series-breaker even if there is no loss of down. Add in the fact fouls by A behind the LOS punish them even more since the penalty is often enforced from that spot. The same distance against the defense has less of an impact. Trying to balance OPI and DPI has inherent unfairness built into it.

I disagree, because unless it was already 4th down, team A has the option to punt, or to otherwise adjust their play, on subsequent downs. Team B has no analogous way to mitigate their own loss of distance. As a coach and fan, distance penalties against the defense always seemed to me more consequential on avg. than those against the offense.

Consider the small but significant change in the game engendered by the adoption of post scrimmage kick enforcement. The choice of yardage tacked on against the team that becomes the defense is relatively attractive compared to repeating the previous down with a penalty against the same team as offense.

First down probability
 

I'm a little cornfused. Can someone with a statistics background better explain this chart?

Advanced NFL Stats: First Down Probability

I would think that break even is at 50%. Also, wish the graph had all the lines. I'm also assuming that .6 on the chart is 60%

The text explains; break-even is 66% (.66 on the chart), because the probability of a new series, given that you start with first-and-ten, is .66 - that is, in the NFL, a team gets a first down (or a TD) two thirds of the time when they start first and ten.

So if they gain 5 yards on first down, you look at second and five on the chart, which (if I'm reading it right) is about .7; we've gone up a little from .66, so that's a success; we're now more likely to get a first down than we were when we started.

However, if they throw an incomplete pass, it's now second and ten; that's something like .52 on the chart. They still are more likely than not to get a first down, but now it's less likely than it was on first down, so that play leaves them worse off (obviously). So that's below the break-even point.

What he means by "break-even" is: is this situation better or worse than first and ten?

We had DPI today on 3rd and 27. First time with the no rule. Nobody complained.