Here is the rule as I found it. It’s clear enough except for the part about swinging after two strikes, what does it mean, “…ball cannot be caught”?
“A BALL is a pitch which does not enter the strike zone in flight and is not struck at by the batter. If the pitch touches the ground and bounces through the strike zone it is a “ball.” If such a pitch touches the batter, he shall be awarded first base. If the batter swings at such a pitch after two strikes, the ball cannot be caught. If the batter hits such a pitch, the ensuing action shall be the same as if he hit the ball in flight.”