If you swing at strike three and it hits your arms, is that a foul ball, are you called out where you stand, or can you run to first base?
You are out for swinging. A swing negates anything else.
From Rule 2.00:
A STRIKE is a legal pitch when so called by the umpire, which—
(a) Is struck at by the batter and is missed;
(b) Is not struck at, if any part of the ball passes through any part of the strike
zone;
(c) Is fouled by the batter when he has less than two strikes;
(d) Is bunted foul;
(e) Touches the batter as he strikes at it;
(f) Touches the batter in flight in the strike zone; or
(g) Becomes a foul tip.
