More info:
7.09
It is interference by a batter or a runner when --
(i) He fails to avoid a fielder who is attempting to field a batted ball, or intentionally interferes with a thrown ball, provided that if two or more fielders attempt to field a batted ball, and the runner comes in contact with one or more of them, the umpire shall determine which fielder is entitled to the benefit of this rule, and shall not declare the runner out for coming in contact with a fielder other than the one the umpire determines to be entitled to field such a ball;
Rule 7.09(i) Comment: When a catcher and batter-runner going to first base have contact when the catcher is fielding the ball, there is generally no violation and nothing should be called. “Obstruction” by a fielder attempting to field a ball should be called only in very flagrant and violent cases because the rules give him the right of way, but of course such “right of way” is not a license to, for example, intentionally trip a runner even though fielding the ball. If the catcher is fielding the ball and the first baseman or pitcher obstructs a runner going to first base “obstruction” shall be called and the base runner awarded first base.
PENALTY FOR INTERFERENCE: The runner is out and the ball is dead.