[Vikesrock]

There is a lot of misinformation in this thread right now.

In Autonomous mode it will be difficult to block balls or robots as you are not allowed to go fully across the centerline. Moving fully across the centerline will result in 2 penalties, plus 2 more penalties and a yellow card if a ball or robot is contacted while fully across the centerline, plus 2 more penalties for any additional balls or robots contacted. <G28>

In Teleoperated mode only one alliance robot may be in the Far zone (the zone near your opponent's goals) per rule <G29>.

There are restrictions regarding the use of active mechanisms above the bumpers (<G45>), so you may not use such a mechanism to block the ball.

There are no restrictions on blocking balls with your bumpers or any other passive mechanism on your robot.

In most cases, robots may be blocked or pushed as much as you wish. If you are pinning the robot (including having one robot block each side of the tunnel) you must back up 6ft. for 3 seconds after each 5 second pin <G39>. Robots in contact with their tower or an elevated alliance partner during the Finale period cannot be defended <G34>. Robots must be given a 10-second grace period from contact when righting themselves or others <G32>.

I believe I have covered most of the common scenarios regarding ball and robot blocking, but as always the manual itself (and the Q&A) is the only source of official information.