You can always tell the improvisers who've worked at ComedySportz. They're the ones who go for a laugh even if it violates the rules of the game they're playing. They never become so involved in the art or the process that they forget they're in front of an audience eager to be entertained. Improv purists tend to put ComedySportz at the bottom of the food chain. On the other hand, audiences--especially rowdy, slightly drunk audiences out for a good time--really get revved up by ComedySportz shows, in which makeshift improv teams square off, each hoping to score the most points. This may explain why ComedySportz branches have thrived in cities not otherwise known for their comedy or their theater: Provo, Utah; Richmond, Virginia; San Jose, California. It was founded in 1984 not in improv-saturated Chicago but in beer-soaked Milwaukee, and didn't open in Chicago until 1987; even today the Chicago franchise--packed as it is with players who've studied at ImprovOlympic, Second City, and the Annoyance--takes its job a little more seriously than other outfits, avoiding easy laughs (sometimes) in favor of deepening character or creating a more interesting scene. Those curious to see the difference between the populist improv style and the more purist Chicago school will get a chance this Friday and Saturday, when a team from the Milwaukee ComedySportz goes head-to-head with a Chicago team. By the way, the Cubs play the Brewers this weekend--and there's a two-for-one discount for those bearing tickets from a game. ComedySportz, 2851 N. Halsted, 773-549-8080. Open run: Thursdays, 8 PM; Fridays-Saturdays, 8 and 10:30 PM. $17.