Well by being driven under the bot, usually you will lose if the other robot was designed to make u go on top of it so that u'll completely lose control of your robot.Then again, we were "driven under" and managed to push the other team out while on top of them yesterday at States. Wish we were going to Nationals but our team is just not there (it's our second year and we're young -- nobody has a driver's license yet!!). The girls built the bot in four weeks (our team's sumobot dude quit right after Regionals so we had to start from scratch) and I hate that it's not an event next year. Oh well, my daughter's 14 so she's got a few more years for it to cycle back around again. That was fun.Well good luck!
In the end it all comes down to who is the better driver. It doesn't matter how much you can push if you can't drive under the other bot...
Mostly, plated robots that get under your bot are wide enough to disable your robot's wheels where you try to back up but the robots are pushing forward as well.
The thing about these robots, once you fall inside the trap, it's really really hard to get out.