Originally, to bring up or raise a child (Stewart was reared by his grandmother). Now: to be taught a lesson in an unforgiving manner in any activity, usually a sport or a video game. Essentially a synonym for "schooled", rear also acts as a double entendre, hinting that the schoolee was done in the butt by the schooler-- thus, the lesson was a costly and painful one.
Shit, man! We reared those 14-year-olds in ball today! I can see why they didn't make the JV squad!