Tom - you appear to follow soccer much more than most. I'm still learning some of the nuances. What would be the disadvantage of Iran packing all their guys in the back end of the field (pitch) and just play for the tie? Of course if a clear break out opportunity arose, take the stab, but otherwise just clog up the front of their goal.
sorry I missed this.
@LionJim provided a good bit of the answer.
In the World Cup, teams are placed in groups of 4. In the first week plus of the tournament, each team plays the other 3 teams in their group. While it's nice to dominate, and win every game with ease, teams don't get any awards for doing that. At the end of the group stage of competition, the top two teams in each group advance to the knockout rounds, where it becomes single elimination until a champion is crowned.
The USA team has not shown a great ability to score goals. However, they probably have more offensive firepower than does Iran. So if you're the Iran coach, it pays to have your team go into a defensive shell (kind of what you described), frustrate the USA, and then hope to score on a quick counter at some point in the game. As
@LionJim indicated, for Iran just getting a tie against the USA doesn't guarantee that they'll finish in the top two of their stage, as Wales could conceivably sneak past Iran in such a scenario if they defeat England. (And as
@LionJim mentioned, the World Cup purposely stages the final group stage games at the same time, so that teams battling to advance don't know what's happening in the other game.)
By next week, when the World Cup is in the knockout stage, playing for a tie is not too smart. Because ties will have to be broken, either in OT or by PKs, where anything can happen. In group stage matches, playing for a tie can be a benefit, but that depends on how the other teams in your bracket do.
I hope that helps.