In the infield, It doesn't matter where a hit ball lands with regards to being fair or foul it is where the ball is first touched or comes to rest.
Before first and third base:
- if the ball is touched over fair territory or comes to rest on fair territory it is a fair ball.
- if the ball is touched over foul territory or comes to rest on foul territory it is a foul ball.
BTW, this is not a foul tip. A foul tip is a ball that is touched by the bat and goes directly to the backcatchers hand or glove and is caught.
BigUmp got in there just ahead of me!