[IbleedPink233]

Well, to block an entire lane, you don't need a thirteen foot robot. All you need to do is make a 9 foot robot - if it lies in the center, then there will only be 2 ft of clearance on either side. 2 ft will not let the average 28in wide + bumpers robot through. 9 ft is reasonable for scoing over the Overpass - especially if you have a 40 inch manipulator. 9 ft is also easily obtained by a 2 section tower/elevator or a rotating arm. Since most robots will have almost no ground clearance, they won't be able to climb over the bot (and will probably earn themselves a penalty if they tried). A Trackball might be able to get through, but could be easily blocked by another alliance member.
However, even though it is "possible," I hope that no one is seriously considering this strategy. It would definitely make the game mind-numbingly boring - 15 seconds of play and 1 minute and 45 seconds of robots doing donuts in their little quadrants. FRC is not boring, so making the game boring would not be in the spirit of FIRST.
Not to mention that the strategy would reduce your engineers and student designers and their work to making a roadblock instead of a game-playing robot.
I am more worried about a robot that is less likely to incur penalties, but still effectively bolck scoring: one that can go up to their opponents' Overpass and fold out a huge shield that prevents all but the highest-thrown Trackballs from hurdling. In theory, it is perfectly legal, as long as the robot doesn't grapple anything and moves out of the way when someone signals to pass. Excellent defense, but once again, makes the game more dry and frustrating, not fun.