This arc with a 4-foot radius is called the restricted area. It was
instituted a couple years ago to stop secondary defensive players from
drawing charging fouls while standing underneath the basket.
The rule reads like this:
"An offensive foul for charging should not be called if the contact is
with a secondary defensive player who has established a defensive
position within a designated restricted area "
?There is an exception. A defender can be legally positioned in the
restricted area and draw a charge in one instance -- if the offensive
player receives the ball within the lower defensive box.?
?The lower defensive box is defined as the area between the 3-foot
posted-up marks on the lane, the bottom tip of the circle and the end
line. So, if your man catches a pass in the post, you can establish
position in the restricted area and draw a charge.?
Coaches complain the officials use the restricted area as a crutch,
automatically whistling a foul on the defender who is in the area --
which isn't the intent of the rule.
The rule book warns against doing that.
"The mere fact that contact occurs in these type of plays, or any
other similar play, does not necessarily mean that a personal foul has
been committed. The officials must decide whether the contact is
negligible and/or incidental, judging each situation separately."
Basketball 101: Restricted area
From NBA Basketball Rules:
?An offensive foul should never be called if the contact is with a
secondary defensive player who has established a defensive position
within a designated "restricted area" near the basket for the purpose
of drawing an offensive foul.
The "restricted area" for this purpose is the area bounded by an arc
with a 4-foot radius measured from the middle of the basket as stated
in nba basketball rules.
EXCEPTION: Any player may be legally positioned within the "restricted
area" if the offensive player receives the ball within the Lower
NBA Basketball Rules
Search terms used:
4-foot arc NBA rules
I hope the information provided is helpful!