Botbash is a robot combat event, in a similar vein to Battlebots and Robot Wars. The biggest difference is its focus. In an attempt to let people with less financial means and engineering skills participate in the sport, Botbash focuses on the smaller end of things. Like Battlebots, it has several weightclasses, but the largest Botbash class is the smallest Battlebots class. The weightclasses are 12lb, 30lb, and 55lb.
Unlike Battlebots, Botbash isn't 100% combat. It also has other competition categories. One is a race where the robot has to negotiate a series of obsticles including pylons to weave around and a ramp to go over, with the robots getting points acording to how long they take. Another is a capture the flag competition, where two robots go one-on-one to see who can knock the cone out of its opponants circle first, with the winner of each match getting points. After these two comes the combat competition, where the robots go one-on-one in a double elimination tournament where they gain points based on their final torunament ranking. The winner is the robot that has the most points between all 3 events.
Another thing Botbash has that Battlebots doesn't is an autonomous competition. People build small (around 1 pound) robots with sensors, which try to negotioate a maze whose pattern isn't revealed until everyone gets there. The winner of this class is the robot that can most reliably and quickly reach the end of the maze.