It’s one of the most difficult calls in basketball, and maybe all of sports.

An offensive player is driving to the basket and a defensive player steps up and there’s a collision.

Is it a charge on the offense? Or a block on the defense?

Rochester native and NCAA referee Jeffrey Anderson breaks it all down in this week’s sports school.

“A charge foul is if I have established legal guarding position- two feet on the floor, facing the opponent. I’m allowed to move to maintain legal defense. So, therefore, I’m allowed to move laterally, obliquely- meaning that’s sliding to the side, and stay in front of him,” says Anderson.

“The charge comes from if he hits me in my torso. If he hasn’t gotten by me and I’m legally guarding him, and you’ve deemed him legally guarding him, then that would be a foul on the offensive player,” he says.

The foul on the defensive player occurs when the defender is not in legal guarding position.

“So, let’s just say we’re driving to the basket, now, I’m not guarding this person and I come over. But I arrive late and there’s contact. That’s where we get our block from. If the dribbler takes off and leaves his feet before the defender gets there, it’s an automatic block,” says Anderson.

It’s a difficult call to get right, one that Anderson says most fans, players, and even coaches don’t get quite right.

“For any person watching the game, see where the defensive person came from and see where the defensive person came from and see what he was doing. Was he already there,” says Anderson. “Was his feet there. If he was there, then, even though it might be your team, if that guy runs him over it’s a charge.”