The NFL's 100th season has brought us one of the most significant rule changes in its history: an expansion of replay into judgment calls. The possible review of pass interference has absorbed most of our outrage oxygen this summer, but a number of other rule changes and points of emphasis are poised to impact the regular season with similar strength.

Let's take a closer look at what to expect for the 2019 NFL season, based on a preseason in which officials exaggerated the new rules in some cases to help players and coaches recognize the changes.

Replay review of pass interference

What's new: Coaches can challenge offensive and defensive pass interference penalties, or non-calls, by throwing their red flag. The in-stadium replay official will initiate reviews in the final two minutes of either half and in overtime, and scoring plays remain an automatic review. To add a flag, the NFL will use a standard that requires clear and obvious visual evidence that a player significantly hindered another from making a play on the ball. To remove a flag, the visual evidence must be clear and obvious that there was no significant hindering.

Preseason impact: There was an average of less than one review for pass interference per game, and 91% came from coaches who largely admitted they were over-challenging to test the system. The details:

• There were 56 total reviews for pass interference in the preseason.

• Fifty-one of the reviews were initiated by coaches, and six resulted in changed calls. Five of those six put a flag on the field.

• Five reviews were initiated by the replay booth. Three resulted in changed calls, two of which put a flag on the field.

What to expect: If preseason is any indication, the rule won't be as disruptive as feared. Three major takeaways emerged.

First, replay officials seemed careful about stopping games for reviews. That could change in the regular season, when outcomes matter and teams are more compelled to pass in the final two minutes. But five stoppages in 65 games was an endurable rate.

Second, it was easier to get a flag added than to have one removed. That shouldn't be surprising given the level of contact between receivers and defenders on most plays.

Third, and perhaps most importantly, senior vice president of officiating Al Riveron upheld 84% of the original calls. That rate should effectively limit challenges from coaches, who don't want to risk a timeout for a frivolous review. It also sent a message to replay officials, who must decide in real time whether to stop a game in some of its most dramatic moments.

One complication to consider is the potential impact of offensive pass interference on scoring plays, which are automatically reviewed. Many teams use tight ends and receivers to clear a path for the intended target, and those players don't always limit the contact to one yard beyond the line of scrimmage as required by the rulebook. Riveron overturned a Cincinnati Bengals touchdown because he saw a tight end blocking downfield during an automatic review.

"In #INDvsCIN, there was clear and obvious visual evidence of offensive pass interference by #86, therefore the ruling on the field of a touchdown was negated due to the foul." -AL pic.twitter.com/adE9ZYjNob

— NFL Officiating () August 30, 2019

Blindside blocks

What's new: All blindside blocks are now illegal. Previously, they were allowed unless the contact was to an opponent's head or neck area. A blindside block is defined as forcible contact toward an opponent with the head, shoulder or forearm when running toward or parallel to the blocker's goal line.

Preseason impact: Because of the expanded definition, there were more flags for blindside blocks during the 2019 preseason (12) than during the entire 2018 regular season (eight).

What to expect: This change will take some adjustment and, at least early in the season, will result in some calls that penalize what look like standard football blocks. The most eye-opening preseason example came from the Detroit Lions-Houston Texans matchup.

"In #DETvsHOU, DET #76 goes back toward his own end-line and forcibly blocks his opponent with his shoulder. By rule, this is a blindside block." -AL pic.twitter.com/idbRBBH8Nk

— NFL Officiating () August 18, 2019

At the start of training camp, the NFL distributed a video that showed three examples of how to avert blindside block penalties. In each case, the player avoided almost all contact and instead simply got in the way of his opponent, forcing a redirect that delayed pursuit of the ball carrier. Such caution will require extreme discretion from players in a game in which they are otherwise encouraged to hit opponents with maximum force.

Offensive holding

What's new: Officials have been asked to make a point of emphasis on instances when linemen wrap their arms around defenders on the backside of running plays. The technique is known to officials as a "lobster block."

Preseason impact: There were 469 holding penalties during the 2019 preseason, a 71% spike from the 2018 preseason. It isn't clear how many were for lobster blocks, but the increase matches those generated by other points of emphasis in previous years.

What to expect: Rates for holding penalties are traditionally higher in the preseason, but it's safe to assume that this spike will travel into at least the first half of the regular season before officials and players adjust. Some players and coaches finished the preseason more concerned about the potential impact of holding penalties than they were about pass interference reviews or blindside blocks.

Officials called an average of 7.2 penalties for offensive holding per game during the preseason. For context, that's more than twice the rate of the 2018 regular season (3.4). Even if the rate drops significantly during the regular season, the overall trend will still lead to an increase in penalties -- at least during the early portion of the season. Historically, penalty spikes associated with points of emphasis fade by midseason as officials and players adjust.

Helmet rule

What's new: Officials have been tasked with paying special attention to a rule that was introduced in 2018 but largely unenforced on the field during the regular season. Players are prohibited from lowering their helmet to initiate contact with an opponent.

Preseason impact: Although they didn't call it as often as in the chaotic 2018 preseason, officials threw more flags for violations of the helmet rule in 65 preseason games (24) than they did during 256 regular-season games in 2018 (18). At the 2019 preseason rate, there would be 92 such penalties during the regular season.

What to expect: This uptick reflected months of rhetoric from the NFL, whose leaders said they expected more enforcement in 2019 as players and officials grew more comfortable with the rule's requirements. That is especially true for offensive players, who were flagged for only one of last season's 18 penalties.

But the rule remains an exceptionally difficult call for officials, in part because it can be difficult to see the contact from beginning to end amid the mass of players running to the ball. The penalty rate is likely to be higher in 2019 than last season, but it probably will fall short of what we saw in either the 2018 or 2019 preseasons.

False start on QBs

What's new: The rule remains unchanged. As stated in the NFL rulebook, "any quick abrupt movement by a single offensive player, or by several offensive players in unison, which simulates the start of the snap, is a false start." An NFL spokesman said it is not a point of emphasis, either. But at times during the preseason, there was notable attention paid to quarterbacks clapping their hands and lifting their legs prior to the snap.

Preseason impact: In the first three weeks of the preseason, officials threw seven flags for false starts on quarterbacks. Five were directed at the Arizona Cardinals: three on backup Brett Hundley and two on starter Kyler Murray. There were a total of nine such penalties called on quarterbacks during the entire 2018 regular season.

What to expect: There have been previous points of emphasis on centers and quarterbacks attempting to draw defenders offsides by simulating action that led to snaps. The focus on the Cardinals indicated this would not be a leaguewide focus, but Green Bay Packers quarterback Aaron Rodgers was flagged in Thursday night's opener for clapping his hands without receiving a snap. Still, it seems likely that teams will adjust early in the season and minimize such calls after the first few weeks.