I really don't think that this is game makes defense impossible, just difficult to play without a plan. While you can't pin other robots, you can push them. There is a wide open area of the field where full contact is allowed. Now if your goal is to absolutely prevent another team from scoring, that may not be possible. But think about this, all of the scoring for an alliance is together on one side of the arena, in the middle, and the sides are off limits to the scoring teams. The scoring zone is more concentrated than a "typical" FRC game. I don't think the good defense is going to be played right outside the opponents scoring zone. I think it will be played as robots try to transition from getting a tube in their lane to the middle of the field.
You can do a lot by making it really difficult for an opponent to make it into the scoring zone. Whenever they exit their own lane, they have to move back into the middle. If they try to go out the end, you just parallel their movement between the towers. They can't go into your lane without getting a penalty, so if you drive well, they have to push out past you. So I am betting that teams without really beefy drive trains will try for the race out the side of their lane into the middle of the field. Again, just try to parallel their movement between the towers. If you lurk by the tower at the corner of your opponents' lane you can move to block their movement to the scoring zone without risking entering their lane.
As I type this I am more firmly convinced that coordinated, planned movement is needed. This may be a year when "offensive blocking" is really important. If your alliance has a really good scoring robot, the other side has a strong incentive to have one of their robots do everything it can to slow that robot down. Some coordinated interference by a teammate might be needed to spring the good scoring bot free.
On the other hand now, getting your minibot down is going to be a challenge. I am thinking that our schools' long armed, 6' 10" center might make a good human player.
