The hillers, because there are lots of hills and stuff. The previous knick-name was the stone throwers....100% serious!! Apparently way back in the day, when visiting teams would drive into town, people would throw stones at the bus.
When I was in school we were called the lancers, but the best one was one of they other local schools the had a contest to let students create a team name. The result was Fairfield Union Charging Knights. That only lasted a season till the administration realized there error in judgment.