When the ball is inbounded with .2 or .1 seconds remaining in an NBA game, a player is not allowed to catch and shoot. They have to tap or dunk the ball. This is the Trent Tucker Rule, and it ensures that in these situations, the only way a team can score is at the rim.
The Detroit Pistons were up by one thanks to this Brandon Jennings floater and the San Antonio Spurs had the ball with .1 seconds left. Mindful of the Tucker rule, Stan Van Gundy knew there was no need for his team to defend anything besides the basket itself. So he employed a special strategy:
We're going to laugh because it's Stan Van Gundy yelling FORM A F****** WALL, but honestly, this is good coaching. Here is the f****** wall they formed:
In the only scenario I've ever seen where a player scored with .1 seconds left, the opposing defense defended the play like a regular possession, allowing David Lee to get loose on a run to the rim. The FORM A F****** WALL defense ensures this doesn't happen and prevents the only legal way of scoring the opponent has left.