Basic baseball question?

I am so confused. Sometimes a hitter drills a ball 50 feet deep, the outfielder catches it, and the hitter is out. Why sometimes can a hitter do the same thing, and a player on base can just run to the next plate and sometimes they can't? Please explain.

2014-06-25T21:31:45Z

I'll rephrase. In my second hypothetical situation, the hitter does the same thing, as in hits it 50 feet in the air, the outfielder catches it, and the plate runner can still run. Why?

mattapan262014-06-25T22:59:12Z

When there are fewer than two outs, a runner on base may attempt to advance to the next base by running as soon as the ball is touched by the fielder. It usually occurs when the runner is on second or third. If the runner is on third and scores when a fly ball is caught, it's called a sacrifice fly and the batter is not charged with an at bat and gets credit for a run batted in. Of course the fielder can try to throw the runner out. Here's an illustration https://www.youtube.com/watch?v=vn2uK5Dh06c

Anonymous2014-06-25T21:55:11Z

This is called at tag up. When there is a runner on first and the outfielder catches the ball he can attempt to advance to second. He can only do so if he tags first after the ball is caught. Sometimes people don't run for the fear of getting out.

carlos2014-06-26T00:01:26Z

It's a sac fly or going halfway to next base in case ball is dropped

Anarchist2014-06-25T21:33:13Z

He is running in the case he drops the ball.