Not it is not, if a OT gets called for holding then it is a 10 yard flag and play never happened. One of the plays I am talking about was the first play of the series and 74 got caught for hold so it should be 1st and 20 not 1st and 18. This is not college.
It's not quite that simple. There are two sets of rules for enforcement of offensive holding. One set of rules is for running plays or after a pass is completed. The other set of rules is for passing plays from the moment of the snap to the moment a forward pass is thrown.
For passing plays the penalty is marked off from the previous spot and the down remains the same.
For running plays/completed passes you first compare the dead ball spot (where the play ended) to the spot of the foul. Whichever is closest to the offense's own endzone is the spot the penalty is marked off from. The down remains the same unless the offense got a first down even after marking off the penalty, in which case it's first-and-10.
So for passing plays the hold will always give you 1st-and-20 in your case, unless a half-the-distance is involved.
But for running plays/completed passes it depends on where the hold was and where the runner/receiver was tackled. If there's a run and the runner gains 18 yards and the hold was 6 yards downfield from the LOS then spot of enforcement is a 6yd gain and after marking off 10yd from there you have a 4yd loss so we have 1st-and-14 after enforcement. Or if the runner ran 12yd and the hold happened a yard downfield of the runner the spot of enforcement is a 12yd gain and after marking off the 10yd penalty you have a 2yd gain, so you have 1st-and-8 after enforcement. Or if the runner ran 21yd and the hold happened at that point the spot of enforcement is a 21yd gain, and marking off the penalty gives an 11yd gain, which is still a first down, so the chains get moved and we revert to 1st-and-10 at that new point. Similar stuff for holds that happen after completed passes.
See Rule 14, Section 1, Article 2, Items 2 and 4; Rule 14 Section 3 (all of it); and Rule 14 Section 4 Articles 2 and 5. (When reading the rulebook the references to "Team A" mean the offense and "Team B" mean the defense). The real rulebook (not just the digest of rules) is available on NFL.com.
