Basically, a runner can run to another base whenever he wants
Good things a batter-runner or runner can do:
- Be aware of when he has to run to a base, and when it is an option.
- Constantly calculate the risk of making an out versus the reward of advancing to another base.
- Steal a base
Bad things a batter-runner or runner can do when
he's at risk and
not touching a base:
- Get tagged out.
- Get forced out, which can only happen if he has been
forced to advance, or he leaves his
base too soon in the case that a fly-ball is caught.