I found that the fastest way to boost this was to set up a battle royal, 3 hits, in the BK parking lot. Have one player go through all 4 blue gate(cones) and then stop. The second person will drive up in front of the first person. The person who went through the gates should activate their shield, and slowly drive into the other player, pushing them a little bit. It will score a hit, and make the person spin out. When the person stops spinning out, it will score another hit, and then a third time.
If you went through all four blue gates, you should have enough to activate shields again, just in case you didn't get all three hits in time.
Each round took 11-13 seconds for me to complete, and when I finished 25 rounds, the achievement unlocked.
Edit 9/28/11 - Credit to Bodz61: It doesn't matter who wins the rounds, as long as you finish them you get credit.