This is the episode where Cliff Clavin truly become the character we all know and love(?). In Season One he was the most vocal of the barflies, but he wasn't established as a bar regular. In his first starring episode (Little Sister Don't Cha), they played up his awkwardness with women. Here we have the real Cliff: a blowhard and a coward, but still someone you'd defend in a bar fight.
A newcomer to the bar (Peter Iancangelo, looking quite a bit like Danny Aiello) decides he's had enough of Cliff's endless blather and challenges him to a fight. Cliff chickens out and returns with Lewis, a large Black coworker with a surly disposition. The bully backs down, until Lewis agrees that Cliff is annoying and leaves.
Some critics have commented on the racial politics of this episode. In a show noted for having a very white cast, it's unfortunate that one of the most memorable roles for a black actor is a tough, scary guy. However, Sam Scarber is pretty funny as Lewis ("How am I supposed to know Leslie Uggams?") and he illustrates Cliff's cowardice perfectly.
This would be enough to make this a classic episode, but the B plot puts it over the top. This is where we learn the infamous Diane Chambers system for sports betting. Diane is obviously trolling Sam, but she's also winning, and Sam accuses her of "destroying the sport of football."
Everybody is in top form here, and Coach gets one of his best lines ("Thanks. I need a brick"). A top ten episode for sure.