trip; slow

A1 gets the ball on the wing. A3 comes up to set a screen on B1. A3 is late getting there and while stepping to set the screen, trips B1 causing him to fall. This is an illegal screen and needs to be called. Rule 4-40-2-a-d states the requirements for a screen to be legal. The screener should be stationary with the feet no wider than shoulder width apart. Neither of these were done by A3 which is what causes this screen to be illegal. Note: When officiating a competitive matchup where a screen is going to be set, use the 70/30 rule. 70% of your focus goes to the screener and 30% goes to the ball handler. This will increase your call percentage on plays such as this.