The North American Soccer League made quite a few changes to the way it played soccer. There were the counting-down clock, the shootout to decide tied games, and a standings system that could award as many as nine points per game depending on the number of goals scored. However, none of those was a change in the basic rules of the game decided by the International Football Association Board and administered by FIFA. The 35-yard line was a different matter. The 35-yard line was a rules-change experiment that did require FIFA approval, and became a serious point of contention in the NASL's relations with the rest of the soccer world.
In 1973, FIFA granted permission for the NASL to experiment with a change in the offside rule, adding a line across the field 35 yards out from the goal, outside which a player couldn't be called offside, even if there were only one defender (presumably the goalkeeper) between him and the goal when the ball was passed to him. The change, an attempt to make the game more appealing to American spectators by injecting some more offense into it, was an alteration of the usual soccer rule that a player couldn't be called offside in his own half of the field. With this change, the zone in which he couldn't be called offside was extended closer to the goal, 20 yards closer on a 110-yard field.
There were critics who said that the change actually hurt the offense. Because forwards could move closer to the goal without being offside, defenders were forced to stay farther back and couldn't as easily join their teams' attack when the situation called for them to move forward. Whether the sum of the two effects helped or hurt the offense was never determined for certain, although supporters of the change pointed out that at the very least, it helped to open up the midfield and make the game less gridlocked.
What was certain was that by 1981, FIFA had become very impatient with the NASL, and by extension with the USSF, for allowing the experiment to extend several years beyond the time FIFA had allotted for it. With the USSF threatened with expulsion from FIFA, which would have made the NASL an outlaw league and thus unable to make lucrative contact with the rest of the soccer world, the league agreed to discontinue the use of the 35-yard line at the end of the 1981 season.
The NASL was definitely not the last American group wishing to alter the rules of the game. Listen to this description from Beau Dure's 2010 book Long-Range Goals about one of the three 1993 bidders for the role of running a first-division league in the United States: "League One America proposed dividing the field into zones marked with chevrons and limiting players to specific zones for an entire period. The color-coded uniforms -- white for a striker, blue for players in the blue zone, yellow for players in the yellow zone, and red for defenders -- would include electronic signaling devices that would tell the referee when a player had veered too far....Coaches would be required to change the lineup for the second period, reassigning players to different zones. Players' decisions to pass or shoot would be complicated by a multiple-point system -- the farther away from the goal your zone was, the more your shot could count. The placement also could affect the scoring -- the league would include a large goal built around an existing soccer goal, with an additional half-point awarded for any shot squeezed between the frames."
Yikes! The 35-yard line seems pretty tame compared to that, doesn't it. Calvinball, anyone?