Carlton and Will are drawing on the basketball chalkboard, teasing each other about their height, brain size, etc. The circle that represents Carlton's big brain changes between shots.
Towards the end of the game at the end of the episode, the coach calls a timeout (makes a "T" with his hands to signal it). But when the referee gives him the timeout, he also makes a "T" with his hands to (wrongly) signal a timeout. In reality, when the ref makes a "T" with his hands it signals a technical foul, so the ref actually slapped the coach with a technical foul.
At the start of the basketball game near the end of the show, you get a glimpse of the top of the gymnasium set and stage lights.
The basketball court is obviously much smaller than regulation size.